正则匹配之贪婪和非贪婪——Python

python贪婪和非贪婪

Python里数量词默认是贪婪的（在少数语言里也可能是默认非贪婪），总是尝试匹配尽可能多的字符；

非贪婪则相反，总是尝试匹配尽可能少的字符。

在"*","?","+","{m,n}"后面加上？，使贪婪变成非贪婪。

>>> s="This is a number 234-235-22-423"
>>> r=re.match(".+(\d+-\d+-\d+-\d+)",s)
>>> r.group(1)
\'4-235-22-423\'
>>> r=re.match(".+?(\d+-\d+-\d+-\d+)",s)
>>> r.group(1)
\'234-235-22-423\'
>>>

>>> re.match(r"aa(\d+)","aa2343ddd").group(1)
\'2343\'
>>> re.match(r"aa(\d+?)","aa2343ddd").group(1)
\'2\'
>>> re.match(r"aa(\d+)ddd","aa2343ddd").group(1) 
\'2343\'
>>> re.match(r"aa(\d+?)ddd","aa2343ddd").group(1)
\'2343\'
>>>