pdb 模块在 python 中的工作原理

import pdb
def combine(s1,s2):      # define subroutine combine, which...
    s3 = s1 + s2 + s1    # sandwiches s2 between copies of s1, ...
    s3 = '"' + s3 +'"'   # encloses it in double quotes,...
    return s3            # and returns it.
a = "aaa"
pdb.set_trace()
b = "bbb"
c = "ccc"
final = combine(a,b)
print final