
>>> import re
>>> re.search("sanchuang","hello world this is sanchuang")
<_sre.SRE_Match object; span=(20, 29), match='sanchuang'>
>>> re.search("sanchuang","hello world this is")
>>> result = re.search("sanchuang","hello world this is")
>>> print(result)
None
>>> re.search("sanchuang","hello world sanchuang this is")
<_sre.SRE_Match object; span=(12, 21), match='sanchuang'>
>>> re.search("sanchuang","hello world,sanchuang  this is sanchuang")
<_sre.SRE_Match object; span=(12, 21), match='sanchuang'>
>>>

re.match -- (只匹配字符串的开始)

• 从字符串头查找匹配项

• 接受一个正则表达式和字符串，从主串第一个字符开始匹配，并返回发现的第一个匹配。

• 如果字符串开始不符合正则表达式，则匹配失败，re.match返回 None


>>> re.search(r"\\\\tsanle","hello\\\\tsanle")
<_sre.SRE_Match object; span=(5, 13), match='\\\\tsanle'>
>>> re.search("\\\\tsanle","hello\\\\tsanle")
<_sre.SRE_Match object; span=(6, 13), match='\\tsanle'>
>>> re.search("\\tsanle","hello\\\tsanle")
<_sre.SRE_Match object; span=(6, 12), match='\tsanle'>
>>>

r'sanle' 中的r代表的是raw（原始字符串）

• 原始字符串与正常字符串的区别是原始字符串不会将\字符解释成一个转义字符

• 正则表达式使用原始字符很常见且有用


>>> msg = "It's raining cats and dogs"
>>> match = re.search(r"cats",msg)
>>> match.start()
13
>>> match.end()
17
>>>

match.group(default=0)：返回匹配的字符串。

• group 是由于正则表达式可以分拆为多个只调出匹配子集的子组。

• 0是默认参数，表示匹配的整个串，n 表示第n个分组 re模块基本用法-match对象

match.start()

• start方法提供了原始字符串中匹配开始的索引

match.end()

• end方法提供了原始字符串中匹配开始的索引 re模块基本用法-match对象

match.groups()

• groups返回一个包含所有小组字符串的元组，从 1 到所含的小组号


>>> import re
>>> re.match("sanchuang","sanchuang hello world this is")
<_sre.SRE_Match object; span=(0, 9), match='sanchuang'>
>>> result1 = re.match("sanchuang","hello world this is ")
>>> print(result1)
None
>>> result2 = re.match("sanchuang","hello world,sanchuang  this is sanchuang")
>>> print(result2)
None
>>>>>> match.groups()
()
>>> match = re.search(r"(cats)",msg)
>>> match.groups()
('cats',)
>>>

findall和finditer：找到多个匹配

re.findall

• 查找并返回匹配的字符串，返回一个列表

re.finditer

• 查找并返回匹配的字符串，返回一个迭代器

能用for i in 循环的都是迭代器


msg = "It's raining cats and dogs, cats1 cats2"
result = re.findall("cats",msg)
print(result)
result2 = re.finditer("cats",msg)
print(result2)
for i in result2:
    print(i.group())
 
结果：
['cats', 'cats', 'cats']
<callable_iterator object at 0x000002267C80B820>
cats
cats
cats
 
 
msg = "It's raining cats and dogs, cats1 cats2"
result3 = re.finditer("cats",msg)
print(list(result3))
 
结果：
[<re.Match object; span=(13, 17), match='cats'>, <re.Match object; span=(28, 32), match='cats'>, <re.Match object; span=(34, 38), match='cats'>]

re.sub('匹配正则','替换内容','string')

• 将string中匹配的内容替换为新内容


msg = "I am learning python"
print(re.sub("python","PYTHON",msg))
 
结果：
I am learning PYTHON

编译正则：re.compile('匹配正则')


msg = "I am learning python"
msg2 = "I am learning Enligsh"
msg3 = "hello world"
reg = re.compile("python")
print(reg.findall(msg))
print(reg.findall(msg2))
print(reg.findall(msg3))
print(re.findall("python",msg))

编译正则的特点：

• 复杂的正则可复用。

• 使用编译正则更方便，省略了参数。

• re模块缓存它即席编译的正则表达式，因此在大多数情况下，使用compile并没有很大

的性能优势

三、基本正则匹配基本正

Ⅰ、则基本正则匹配 - 区间匹配

区间：[]

• 正则匹配区分大小写

• 匹配所有字母：[a-zA-Z]

• 匹配所有字母及-：[a-zA-Z\-]


ret = re.findall("python","Pyhton 3 python")
print(ret)
ret1 = re.findall("[Ppfg]ython","Python 3 python fython Fython")
print(ret1)
ret2  = re.findall("[a-zA-Z\-]","abcABC-123-")
print(ret2)
 
结果：
['python']
['Python', 'python', 'fython']
['a', 'b', 'c', 'A', 'B', 'C', '-', '-']

匹配a或b：a|b

• 匹配cat或dog


msg = "It's raining cats and dogs"
ret = re.search("cats|dogs",msg)
print(ret.group())
ret1 = re.findall("cats|dogs",msg)
print(ret1)
 
结果：
cats
['cats', 'dogs']

 #re.search  查找匹配第一个    #re.findall  查找匹配全部

取反：[^abc]

• 匹配a+非小写字母


ret = re.findall("[0-z]","lab3cb3ala#>=？！aB")
print(ret)
ret1 = re.findall("[^0-9A-Za-z]","lab3cb3al#>=?!aB")
print(ret1)
ret2 = re.findall("a[^a-z]","lab3cb3al#>=?!aB")
print(ret2)
 
结果：
['l', 'a', 'b', '3', 'c', 'b', '3', 'a', 'l', 'a', '>', '=', 'a', 'B']
['#', '>', '=', '?', '!']
['aB']

任意字符：“.”占位符

• 匹配任何（除\n外）的单个字符，它仅仅只以出现在方括号字符组以外


ret = re.findall("p.thon","python pYTHON Python pYthon Pthon p=thon")
print(ret)
ret = re.findall("p.thon","python pYTHON Python pYthon Pthon p thon p\nthon")
print(ret)
 
结果：
['python', 'pYthon', 'p=thon']
['python', 'pYthon', 'p thon']

快捷方式

快捷标识	功能
\A	匹配字符串开始
\bword\b	词边界
\w	匹配包括下划线的任何单词字符。等价于'[A-Za-z0-9_]'
\W	匹配任何非单词字符。等价于 '[^A-Za-z0-9_]'
\d	匹配一个数字字符。等价于 [0-9]
\D	匹配一个非数字字符。等价于 [^0-9]
\s	匹配任何空白字符，包括空格、制表符、换页符等等。等价于 [ \f\n\r\t\v]
\S	匹配任何非空白字符。等价于 [^ \f\n\r\t\v]

例子如下：（使用快捷键得加“r”）


## \bword\b ## ---数字、字符、下划线不算做边界
ret = re.finditer(r"\bworld","hello world 123world =world  world123 ##world## abcworldabc")
print(list(ret))
ret1 = re.finditer(r"world\b","hello world 123world =world  world123 ##world## abcworldabc")
print(list(ret1))
ret2 = re.finditer(r"\bworld\b","hello world 123world =world  world123 ##world## abcworldabc")
print(list(ret2))
 
结果：
[<re.Match object; span=(6, 11), match='world'>, <re.Match object; span=(22, 27), match='world'>, <re.Match object; span=(29, 34), match='world'>, <re.Match object; span=(40, 45), match='world'>]
[<re.Match object; span=(6, 11), match='world'>, <re.Match object; span=(15, 20), match='world'>, <re.Match object; span=(22, 27), match='world'>, <re.Match object; span=(40, 45), match='world'>]
[<re.Match object; span=(6, 11), match='world'>, <re.Match object; span=(22, 27), match='world'>, <re.Match object; span=(40, 45), match='world'>]

 \B 匹配一个前后都无单词边界的字符串


ret = re.finditer(r"\Bworld\B","hello _world world123 123world =world ##world## abcworldabc")
print(list(ret))
 
结果：
[<re.Match object; span=(51, 56), match='world'>]


# \w \W
ret = re.findall(r'\w',"python3#")
print(ret)
ret = re.findall(r'\W',"python3#")
print(ret)
 
结果：
['p', 'y', 't', 'h', 'o', 'n', '3']
['#']

开始与结束：^, $

• 匹配以python开头：^python

• 匹配以python结尾：python$


ret = re.findall("^python","hello python")
print(ret)
ret1 = re.findall("^python","python123#")
print(ret1)
ret2 = re.findall("python$","hello python")
print(ret2)
ret3 = re.findall("^python$","hello python")
print(ret3)
 
结果：
[]
['python']
['python']
[]

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