什么是 Python 代码中的编译

#!/usr/bin/env python
import re
from time import ctime
def run():
        pattern='case'
        rere_obj=re.compile(pattern)
        infile=open('/etc/rc.subr','r')
        match_count=0
        lines=0
        for line in infile:
                match=re_obj.search(line)
                if match:
                        match_count+=1
                lines+=1
        return (lines,match_count)
if __name__=='__main__':
        print('starting at:',ctime())
        lines,match_count=run()
        print "LINES:",lines
        print "MATCHS:",match_count
        print('ending at:',ctime())