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30段极简Python代码：这些小技巧你都Get了么

选自 | towardsdatascience
转自 | 机器之心

30段极简Python代码：这些小技巧你都Get了么

Python 是机器学习最广泛采用的编程语言，它最重要的优势在于编程的易用性。如果读者对基本的 Python 语法已经有一些了解，那么这篇文章可能会给你一些启发。作者简单概览了 30 段代码，它们都是平常非常实用的技巧，我们只要花几分钟就能从头到尾浏览一遍。


1. 重复元素判定


以下方法可以检查给定列表是不是存在重复元素，它会使用 set() 函数来移除所有重复元素。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;">def all_unique(lst):<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    return len(lst) == len(set(lst))<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />x = [1,1,2,2,3,2,3,4,5,6]<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />y = [1,2,3,4,5]<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />all_unique(x) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># False</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />all_unique(y) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># True</span></p>


2. 字符元素组成判定


检查两个字符串的组成元素是不是一样的。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;"><span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">from</span> collections <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">import</span> Counter<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-function" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"><span class="hljs-keyword" style="word-wrap: inherit !important;word-break: inherit !important;">def</span> <span class="hljs-title" style="line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">anagram(first, second)</span>:</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">return</span> Counter(first) == Counter(second)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />anagram(<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"abcd3"</span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"3acdb"</span>) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># True</span></p>






3. 内存占用


下面的代码块可以检查变量 variable 所占用的内存。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;"><span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">import</span> sys <br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />variable = <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">30</span> <br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-built_in" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">print</span>(sys.getsizeof(variable)) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># 24</span></p>

4. 字节占用


下面的代码块可以检查字符串占用的字节数。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;"><span class="hljs-function" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"><span class="hljs-keyword" style="word-wrap: inherit !important;word-break: inherit !important;">def</span> <span class="hljs-title" style="line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">byte_size(string)</span>:</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">return</span>(len(string.encode(<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> utf-8 </span>)))<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />byte_size(<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> 😀 </span>) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># 4</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />byte_size(<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> Hello World </span>) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># 11   </span></p>

5. 打印 N 次字符串


该代码块不需要循环语句就能打印 N 次字符串。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;">n = 2; <br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />s =<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"Programming"</span>; <br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />print(s * n);<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># ProgrammingProgramming  </span></p>

6. 大写第一个字母


以下代码块会使用 title() 方法，从而大写字符串中每一个单词的首字母。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;">s = <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"programming is awesome"</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />print(s.title())<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># Programming Is Awesome</span></p>


7. 分块


给定具体的大小，定义一个函数以按照这个大小切割列表。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;"><span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">from</span> math <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">import</span> ceil<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-function" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"><span class="hljs-keyword" style="word-wrap: inherit !important;word-break: inherit !important;">def</span> <span class="hljs-title" style="line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">chunk(lst, size)</span>:</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">return</span> list(<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />        map(<span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">lambda</span> x: lst[x * size:x * size + size],<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />            list(range(<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">0</span>, ceil(len(lst) / size)))))<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />chunk([<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">1</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">2</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">3</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">4</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">5</span>],<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">2</span>)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># [[1,2],[3,4],5]</span></p>

8. 压缩


这个方法可以将布尔型的值去掉，例如（False，None，0，“”），它使用 filter() 函数。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;"><span class="hljs-function" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"><span class="hljs-keyword" style="word-wrap: inherit !important;word-break: inherit !important;">def</span> <span class="hljs-title" style="line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">compact(lst)</span>:</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">return</span> list(filter(bool, lst))<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />compact([<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">0</span>, <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">1</span>, <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">False</span>, <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">2</span>, , <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">3</span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> a </span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> s </span>, <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">34</span>])<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># [ 1, 2, 3,  a ,  s , 34 ]</span></p>

9. 解包


如下代码段可以将打包好的成对列表解开成两组不同的元组。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;"><span class="hljs-built_in" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">array</span> = [[<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> a </span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> b </span>], [<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> c </span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> d </span>], [<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> e </span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> f </span>]]<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />transposed = zip(*<span class="hljs-built_in" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">array</span>)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />print(transposed)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /># [(<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> a </span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> c </span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> e </span>), (<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> b </span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> d </span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> f </span>)]</p>


10. 链式对比


我们可以在一行代码中使用不同的运算符对比多个不同的元素。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;">a = 3<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-built_in" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">print</span>( 2 < a < 8) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># True</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-built_in" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">print</span>(1 == a < 2) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># False</span></p>


11. 逗号连接


下面的代码可以将列表连接成单个字符串，且每一个元素间的分隔方式设置为了逗号。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;">hobbies = [<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"basketball"</span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"football"</span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"swimming"</span>]<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />print(<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"My hobbies are: "</span> + <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">", "</span>.join(hobbies))<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># My hobbies are: basketball, football, swimming</span></p>


12. 元音统计


以下方法将统计字符串中的元音 (‘a’, ‘e’, ‘i’, ‘o’, ‘u’) 的个数，它是通过正则表达式做的。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;"><span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">import</span> re<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-function" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"><span class="hljs-keyword" style="word-wrap: inherit !important;word-break: inherit !important;">def</span> <span class="hljs-title" style="line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">count_vowels(str)</span>:</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">return</span> len(len(re.findall(<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">r [aeiou] </span>, str, re.IGNORECASE)))<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />count_vowels(<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> foobar </span>) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># 3</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />count_vowels(<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> gym </span>) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># 0</span></p>


13. 首字母小写


如下方法将令给定字符串的第一个字符统一为小写。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;"><span class="hljs-function" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"><span class="hljs-keyword" style="word-wrap: inherit !important;word-break: inherit !important;">def</span> <span class="hljs-title" style="line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">decapitalize(string)</span>:</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">return</span> str[:<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">1</span>].lower() + str[<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">1</span>:]<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />decapitalize(<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> FooBar </span>) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">#  fooBar</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />decapitalize(<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> FooBar </span>) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">#  fooBar</span></p>

14. 展开列表


该方法将通过递归的方式将列表的嵌套展开为单个列表。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;"><span class="hljs-function" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"><span class="hljs-keyword" style="word-wrap: inherit !important;word-break: inherit !important;">def</span> <span class="hljs-title" style="line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">spread(arg)</span>:</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    ret = []<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">for</span> i <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">in</span> arg:<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />        <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">if</span> isinstance(i, list):<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />            ret.extend(i)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />        <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">else</span>:<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />            ret.append(i)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">return</span> ret<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-function" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"><span class="hljs-keyword" style="word-wrap: inherit !important;word-break: inherit !important;">def</span> <span class="hljs-title" style="line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">deep_flatten(lst)</span>:</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    result = []<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    result.extend(<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />        spread(list(map(<span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">lambda</span> x: deep_flatten(x) <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">if</span> type(x) == list <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">else</span> x, lst))))<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">return</span> result<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />deep_flatten([<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">1</span>, [<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">2</span>], [[<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">3</span>], <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">4</span>], <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">5</span>]) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># [1,2,3,4,5]</span></p>


15. 列表的差


该方法将返回第一个列表的元素，其不在第二个列表内。如果同时要反馈第二个列表独有的元素，还需要加一句 set_b.difference(set_a)。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;">def difference(a, b):<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    set_a = <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">set</span>(a)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    set_b = <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">set</span>(b)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    comparison = set_a.difference(set_b)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">return</span> <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">list</span>(comparison)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">difference</span>([<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">1</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">2</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">3</span>], [<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">1</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">2</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">4</span>]) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># [3]</span></p>


16. 通过函数取差


如下方法首先会应用一个给定的函数，然后再返回应用函数后结果有差别的列表元素。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;"><span class="hljs-function" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"><span class="hljs-keyword" style="word-wrap: inherit !important;word-break: inherit !important;">def</span> <span class="hljs-title" style="line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">difference_by(a, b, fn)</span>:</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    b = set(map(fn, b))<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">return</span> [item <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">for</span> item <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">in</span> a <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">if</span> fn(item) <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">not</span> <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">in</span> b]<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">from</span> math <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">import</span> floor<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />difference_by([<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">2.1</span>, <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">1.2</span>], [<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">2.3</span>, <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">3.4</span>],floor) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># [1.2]</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />difference_by([{ <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> x </span>: <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">2</span> }, { <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> x </span>: <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">1</span> }], [{ <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> x </span>: <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">1</span> }], <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">lambda</span> v : v[<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> x </span>])<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># [ { x: 2 } ]</span></p>


17. 链式函数调用


你可以在一行代码内调用多个函数。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;"><span class="hljs-function" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"><span class="hljs-keyword" style="word-wrap: inherit !important;word-break: inherit !important;">def</span> <span class="hljs-title" style="line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">add(a, b)</span>:</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">return</span> a + b<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-function" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"><span class="hljs-keyword" style="word-wrap: inherit !important;word-break: inherit !important;">def</span> <span class="hljs-title" style="line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">subtract(a, b)</span>:</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">return</span> a - b<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />a, b = <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">4</span>, <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">5</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />print((subtract <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">if</span> a > b <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">else</span> add)(a, b)) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># 9 </span></p>


18. 检查重复项


如下代码将检查两个列表是不是有重复项。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;">def has_duplicates(lst):<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    return len(lst) != len(set(lst))<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />x = [1,2,3,4,5,5]<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />y = [1,2,3,4,5]<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />has_duplicates(x) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># True</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />has_duplicates(y) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># False</span></p>


19. 合并两个字典


下面的方法将用于合并两个字典。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;"><span class="hljs-function" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"><span class="hljs-keyword" style="word-wrap: inherit !important;word-break: inherit !important;">def</span> <span class="hljs-title" style="line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">merge_two_dicts(a, b)</span>:</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    c = a.copy()   <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># make a copy of a </span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    c.update(b)    <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># modify keys and values of a with the ones from b</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">return</span> c<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />a = { <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> x </span>: <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">1</span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> y </span>: <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">2</span>}<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />b = { <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> y </span>: <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">3</span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> z </span>: <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">4</span>}<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />print(merge_two_dicts(a, b))<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># { y : 3,  x : 1,  z : 4}</span></p>


在 Python 3.5 或更高版本中，我们也可以用以下方式合并字典：


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;"><span class="hljs-function" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">def <span class="hljs-title" style="line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">merge_dictionaries(a, b)</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />   <span class="hljs-keyword" style="word-wrap: inherit !important;word-break: inherit !important;">return</span> </span>{**a, **b}<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />a = { <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> x </span>: <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">1</span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> y </span>: <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">2</span>}<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />b = { <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> y </span>: <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">3</span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> z </span>: <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">4</span>}<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />print(merge_dictionaries(a, b))<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /># {<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> y </span>: <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">3</span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> x </span>: <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">1</span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> z </span>: <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">4</span>}</p>


20. 将两个列表转化为字典


如下方法将会把两个列表转化为单个字典。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;">def to_dictionary(<span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">keys</span>, <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">values</span>):<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">return</span> dict(zip(<span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">keys</span>, <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">values</span>))<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">keys</span> = [<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"a"</span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"b"</span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"c"</span>]    <br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">values</span> = [<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">2</span>, <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">3</span>, <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">4</span>]<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">print</span>(to_dictionary(<span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">keys</span>, <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">values</span>))<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># { a : 2,  c : 4,  b : 3}</span></p>


21. 使用枚举


我们常用 For 循环来遍历某个列表，同样我们也能枚举列表的索引与值。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;">list = [<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"a"</span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"b"</span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"c"</span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"d"</span>]<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">for</span> index, element <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">in</span> enumerate(list): <br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-built_in" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">print</span>(<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"Value"</span>, element, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"Index "</span>, index, )<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /># (<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> Value </span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> a </span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> Index  </span>, <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">0</span>)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /># (<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> Value </span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> b </span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> Index  </span>, <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">1</span>)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />#(<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> Value </span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> c </span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> Index  </span>, <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">2</span>)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /># (<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> Value </span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> d </span>, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> Index  </span>, <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">3</span>)    </p>

22. 执行时间


如下代码块可以用来计算执行特定代码所花费的时间。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;">import time<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />start_time = time.time()<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />a = 1<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />b = 2<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />c = a + b<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />print(c) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">#3</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />end_time = time.time()<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />total_time = end_time - start_time<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-section" style="box-sizing: border-box;font-size: inherit;color: rgb(165, 218, 45);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">print("Time: ", total_time)</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># ( Time:  , 1.1205673217773438e-05)  </span></p>

23.Try else


我们在使用 try/except 语句的时候也可以加一个 else 子句，如果没有触发错误的话，这个子句就会被运行。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;"><span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">try</span>:<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">2</span>*<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">3</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">except</span> TypeError:<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    print(<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"An exception was raised"</span>)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">else</span>:<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    print(<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"Thank God, no exceptions were raised."</span>)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">#Thank God, no exceptions were raised.</span></p>

24. 元素频率


下面的方法会根据元素频率取列表中最常见的元素。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;">def most_frequent(<span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">list</span>):<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">return</span> max(set(<span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">list</span>), key = <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">list</span>.count)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">list</span> = [<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">1</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">2</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">1</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">2</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">3</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">2</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">1</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">4</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">2</span>]<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />most_frequent(<span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">list</span>)  </p>

25. 回文序列


以下方法会检查给定的字符串是不是回文序列，它首先会把所有字母转化为小写，并移除非英文字母符号。最后，它会对比字符串与反向字符串是否相等，相等则表示为回文序列。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;"><span class="hljs-function" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"><span class="hljs-keyword" style="word-wrap: inherit !important;word-break: inherit !important;">def</span> <span class="hljs-title" style="line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">palindrome(string)</span>:</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">from</span> re <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">import</span> sub<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    s = sub(<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> [W_] </span>, , string.lower())<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">return</span> s == s[::<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">-1</span>]<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />palindrome(<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> taco cat </span>) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># True</span></p>

26. 不使用 if-else 的计算子


这一段代码可以不使用条件语句就实现加减乘除、求幂操作，它通过字典这一数据结构实现：


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;"><span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">import</span> <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">operator</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />action = {<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"+"</span>: <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">operator</span>.add,<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"-"</span>: <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">operator</span>.sub,<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"/"</span>: <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">operator</span>.truediv,<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"*"</span>: <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">operator</span>.mul,<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">"**"</span>: <span class="hljs-built_in" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">pow</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />}<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />print(action[<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> - </span>](<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">50</span>, <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">25</span>)) # <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">25</span></p>

27.Shuffle


该算法会打乱列表元素的顺序，它主要会通过 Fisher-Yates 算法对新列表进行排序：


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;"><span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">from</span> copy <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">import</span> deepcopy<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">from</span> random <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">import</span> randint<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-function" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"><span class="hljs-keyword" style="word-wrap: inherit !important;word-break: inherit !important;">def</span> <span class="hljs-title" style="line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">shuffle(lst)</span>:</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    temp_lst = deepcopy(lst)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    m = len(temp_lst)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">while</span> (m):<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />        m -= <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">1</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />        i = randint(<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">0</span>, m)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />        temp_lst[m], temp_lst[i] = temp_lst[i], temp_lst[m]<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">return</span> temp_lst<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />foo = [<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">1</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">2</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">3</span>]<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />shuffle(foo) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># [2,3,1] , foo = [1,2,3]</span></p>

28. 展开列表


将列表内的所有元素，包括子列表，都展开成一个列表。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;"><span class="hljs-function" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"><span class="hljs-keyword" style="word-wrap: inherit !important;word-break: inherit !important;">def</span> <span class="hljs-title" style="line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">spread(arg)</span>:</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    ret = []<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">for</span> i <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">in</span> arg:<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />        <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">if</span> isinstance(i, list):<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />            ret.extend(i)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />        <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">else</span>:<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />            ret.append(i)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />    <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">return</span> ret<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />spread([<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">1</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">2</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">3</span>,[<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">4</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">5</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">6</span>],[<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">7</span>],<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">8</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">9</span>]) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># [1,2,3,4,5,6,7,8,9]</span></p>

29. 交换值


不需要额外的操作就能交换两个变量的值。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;"><span class="hljs-function" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"><span class="hljs-keyword" style="word-wrap: inherit !important;word-break: inherit !important;">def</span> <span class="hljs-title" style="line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">swap(a, b)</span>:</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />  <span class="hljs-keyword" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">return</span> b, a<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />a, b = <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">-1</span>, <span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">14</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />swap(a, b) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># (14, -1)</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  />spread([<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">1</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">2</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">3</span>,[<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">4</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">5</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">6</span>],[<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">7</span>],<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">8</span>,<span class="hljs-number" style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">9</span>]) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># [1,2,3,4,5,6,7,8,9]</span></p>


30. 字典默认值


通过 Key 取对应的 Value 值，可以通过以下方式设置默认值。如果 get() 方法没有设置默认值，那么如果遇到不存在的 Key，则会返回 None。


<p style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow-x: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;overflow-y: auto !important;">d = {<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> a </span>: 1, <span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> b </span>: 2}<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /><span class="hljs-built_in" style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;">print</span>(d.get(<span class="hljs-string" style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"> c </span>, 3)) <span class="hljs-comment" style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"># 3</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;word-wrap: inherit !important;word-break: inherit !important;"  /></p>

参考链接：https://towardsdatascience.com/30-helpful-python-snippets-that-you-can-learn-in-30-seconds-or-less-69bb49204172

—完—

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