Python正则表达式元字符

元字符被视为正则表达式的构建块。正则表达式是用于匹配字符串中字符组合的模式。元字符在查找模式方面具有特殊意义，主要用于定义搜索条件和任何文本操作。

一些最常用的元字符及其用途如下：

Meta Character	Description	Example
\d	whole numbers( 0-9 )(single digit)	\d = 7,  \d\d=77
\w	alphanumeric character	\w\w\w\w = geek \w\w\w =! geek
*	0 or more characters	s*  = _,s,ss,sss,ssss…..
+	1 or more characters	s+ = s,ss,sss,ssss…..
?	0 or 1 character	s?  = _ or s
{m}	occurs “m” times	sd{3} = sddd
{m,n}	min “m” and max “n” times	sd{2,3}=sdd or sddd
\W	symbols	\W = %
[a-z]  or [0-9]	character set	geek[sy] = geeky geek[sy] != geeki

正则表达式可以由元字符构建，模式可以使用Python中称为“re”的正则表达式库进行处理。

import re  # used to import regular expressions

内置库可用于编译模式、查找模式、 等等。

示例：在下面的代码中，我们将根据给定的正则表达式生成所有模式

Python3

import re
  
  
'''
Meta characters - 
* - 0 or more
+ - 1 or more
? - 0 or 1
{m} - m times
{m,n} - min m and max n
'''
  
test_phrase = 'sddsd..sssddd...sdddsddd...dsds...dsssss...sdddd'
test_patterns = [r'sd*',        # s followed by zero or more d's
                 r'sd+',          # s followed by one or more d's
                 r'sd?',          # s followed by zero or one d's
                 r'sd{3}',        # s followed by three d's
                 r'sd{2,3}',      # s followed by two to three d's
                 ]
  
  
def multi_re_find(test_patterns, test_phrase):
    for pattern in test_patterns:
        compiledPattern = re.compile(pattern)
        print('finding {} in test_phrase'.format(pattern))
        print(re.findall(compiledPattern, test_phrase))
  
  
multi_re_find(test_patterns, test_phrase)

输出：

finding sd* in test_phrase
[‘sdd’, ‘sd’, ‘s’, ‘s’, ‘sddd’, ‘sddd’, ‘sddd’, ‘sd’, ‘s’, ‘s’, ‘s’, ‘s’, ‘s’, ‘s’, ‘sdddd’]
finding sd+ in test_phrase
[‘sdd’, ‘sd’, ‘sddd’, ‘sddd’, ‘sddd’, ‘sd’, ‘sdddd’]
finding sd? in test_phrase
[‘sd’, ‘sd’, ‘s’, ‘s’, ‘sd’, ‘sd’, ‘sd’, ‘sd’, ‘s’, ‘s’, ‘s’, ‘s’, ‘s’, ‘s’, ‘sd’]
finding sd{3} in test_phrase
[‘sddd’, ‘sddd’, ‘sddd’, ‘sddd’]
finding sd{2,3} in test_phrase
[‘sdd’, ‘sddd’, ‘sddd’, ‘sddd’, ‘sddd’]