Python正则表达式子模式扩展语法与应用

正则表达式语法实际上是独立于任何语言的，在大多数编程语言都可以使用相同的语法。常见正则表达式语法请参考Python使用正则表达式处理字符串

正则表达式使用圆括号“()”表示一个子模式，圆括号内的内容作为一个整体对待，例如'(red)+'可以匹配'redred'、'redredred'等一个或多个重复'red'的情况。使用子模式扩展语法可以实现更加复杂的字符串处理功能。

常用子模式扩展语法

>>> import re

>>> m = re.match(r"(?P<first_name>\w+) (?P<last_name>\w+)", "Malcolm Reynolds")

>>> m.group('first_name')    #使用命名的子模式

'Malcolm'

>>> m.group('last_name')

'Reynolds'

>>> m = re.match(r"(\d+)\.(\d+)", "24.1632")

>>> m.groups()      #返回所有匹配的子模式（不包括第0个）

('24', '1632')

>>> m = re.match(r"(?P<first_name>\w+) (?P<last_name>\w+)", "Malcolm Reynolds")

>>> m.groupdict()      #以字典形式返回匹配的结果

{'first_name': 'Malcolm', 'last_name': 'Reynolds'}

>>> exampleString = '''There should be one-- and preferably only one --obvious way to do it.

Although that way may not be obvious at first unless you're Dutch.

Now is better than never.

Although never is often better than right now.'''

>>> pattern = re.compile(r'(?<=\w\s)never(?=\s\w)') #查找不在句子开头和结尾的never

>>> matchResult = pattern.search(exampleString)

>>> matchResult.span()

(172, 177)

>>> pattern = re.compile(r'(?<=\w\s)never') #查找位于句子末尾的单词

>>> matchResult = pattern.search(exampleString)

>>> matchResult.span()

(156, 161)

>>> pattern = re.compile(r'(?:is\s)better(\sthan)') #查找前面是is的better than组合

>>> matchResult = pattern.search(exampleString)

>>> matchResult.span()

(141, 155)

>>> matchResult.group(0)           #组0表示整个模式

'is better than'

>>> matchResult.group(1)

' than'

>>> pattern = re.compile(r'\b(?i)n\w+\b') #查找以n或N字母开头的所有单词

>>> index = 0

>>> while True:

     matchResult = pattern.search(exampleString, index)

     if not matchResult:

          break

     print(matchResult.group(0), ':', matchResult.span(0))

     index = matchResult.end(0)

not : (92, 95)

Now : (137, 140)

never : (156, 161)

never : (172, 177)

now : (205, 208)

>>> pattern = re.compile(r'(?<!not\s)be\b')       #查找前面没有单词not的单词be

>>> index = 0

>>> while True:

     matchResult = pattern.search(exampleString, index)

     if not matchResult:

          break

     print(matchResult.group(0), ':', matchResult.span(0))

     index = matchResult.end(0)

be : (13, 15)

>>> exampleString[13:20]    #验证一下结果是否正确

'be one-'

>>> pattern = re.compile(r'(\b\w*(?P<f>\w+)(?P=f)\w*\b)') #匹配有连续相同字母的单词

>>> index = 0

>>> while True:

      matchResult = pattern.search(exampleString, index)

      if not matchResult:

           break

      print(matchResult.group(0), ':', matchResult.group(2))

      index = matchResult.end(0) + 1

unless : s

better : t

better : t

>>> s = 'aabc abcd abbcd abccd abcdd'

>>> p = re.compile(r'(\b\w*(?P<f>\w+)(?P=f)\w*\b)')

>>> p.findall(s)

[('aabc', 'a'), ('abbcd', 'b'), ('abccd', 'c'), ('abcdd', 'd')]

>>> s = "It's a very good good idea"

>>> re.sub(r'(\b\w+) \1', r'\1', s)  #处理连续的重复单词

"It's a very good idea"

>>> re.sub(r'((\w+) )\1', r'\2', s)

"It's a very goodidea"