正则表达式

Posted 2021-11-07 nanjingli

1.正则表达式大全

https://www.cnblogs.com/xudong-bupt/p/3586889.html

2.贪婪匹配

*?, +?, ??

The ‘*‘, ‘+‘, and ‘?‘ qualifiers are all greedy; they match as much text as possible. Sometimes this behaviour isn’t desired; if the RE <.*> is matched against ‘<a> b <c>‘, it will match the entire string, and not just ‘<a>‘. Adding ? after the qualifier makes it perform the match in non-greedy or minimal fashion; as few characters as possible will be matched. Using the RE <.*?> will match only ‘<a>‘.

是否需要贪婪匹配在写正则表达式时是很重要的一个概念。‘?‘只有在上面三种表达时才表示非贪婪匹配，其他时候都是表示0个或1个字符。贪婪匹配简单来说就是匹配尽可能多符合的结果，非贪婪匹配表示只要匹配到一个符合的结果就行。下面这个程序是用来匹配前几个字符串是包含数字的的字符串，用来提取数字，数字可以包含正负号，如“+2356 wqrvg”：

 1 import re
 2 class Solution:
 3     def myAtoi(self, str: str) -> int:
 4         str = str.strip()
 5         group = re.match(r‘(([-\\+]\\d+)|\\d+).?‘, str)
 6         if group is None:
 7             return 0
 8         temp = group.groups()
 9         temp1 = int(temp[0])
10         temp2 = pow(2, 31)
11         if temp1 > (temp2 - 1):
12             return temp2-1
13         elif(temp1 < (-1*temp2)):
14             return -1*temp2
15         return temp1