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2. 正则中特殊符号所代表的含义与例子

  1. . 点

    • 不包括换行
      	import re
	ret = re.match(".*","hello\\\nhello")
	print(ret.group())
    • 包括换行
      	import re
	ret = re.match(".*","hello\\\nhello",re.DOTALL)
	print(ret.group())

    re.DOTALL表示匹配所以字符。

  2. ^ 行首

    • 普通行首
      	import re
	ret = re.match("^hel.*","hello\\\nhello")
	print(ret.group())
    • 多行匹配
      	import re
	ret = re.match("^hel.*\n^hel.*","hello\\\nhello",re.MULTILINE)
	print(ret.group())
      注意:这里有两个^,以及添加了re.MULTILINE

  3. $ 行末尾

    • 非多行
      	import re
	ret = re.findall(".+$","hello world\\\nhello")
	print(ret)
    • 多行
      	import re
	ret = re.findall(".+$","hello world\\\nhello",re.MULTILINE)
	print(ret)

  4. * 贪婪匹配

    	import re
	ret = re.findall(".*","hello world\\\nhello")
	print(ret)

  5. + 多个

    	import re
	ret = re.findall(".+","hello world\\\nhello")
	print(ret)

  6. ? 0或1

    	import re
	ret = re.findall(".?","hello world\\\nhello")
	print(ret)

  7. *? +? ??非贪婪匹配,尽量少的匹配

    • 贪婪模式
      	import re
	ret = re.findall("<.*>","<html></html>")
	print(ret)
    • 非贪婪模式
      	import re
	ret = re.findall("<.*?>","<html></html>")
	print(ret)

  8. {m} 严格匹配m个重复字符

    	import re
	ret = re.findall("a{1}","a<html>a</html>")
	print(ret)

  9. {m,n} 至少m个，最多n个。

    	import re
	ret = re.findall("a{1,5}","aaaaa<html>a</html>")
	print(ret)

  10. {m,n}?非贪婪模式匹配

    import re
ret = re.findall("a{1,5}?","aaaaa<html>a</html>")
print(ret)

  11. []集合中任选一个

    • 一一列举
      	import re
	ret = re.findall("[a<]+","aaaaa<html>a</html>")
	print(ret)
    • 范围罗列
      	import re
	ret = re.findall("[a-z]+","aaaaa<html>a</html>")
	print(ret)
    • 集合
      	import re
	ret = re.findall("[\\w]+","aaaaa<html>a</html>")
	print(ret)
    • 取反
      	import re
	ret = re.findall("[^\\w]+","aaaaa<html>a</html>")
	print(ret)

  12. | 多个表达式,从左往右匹配。

    import re
ret = re.findall("(a|h)+","aaaaa<html>a</html>")
print(ret)

  13. (...) 创建组

    import re
ret = re.search("(<html>)a\\1","aaaaa<html>a<html>")
print(ret)

  14. (?...) 不创建组

  15. (?aiLmsux) 局部按照特殊规则处理

  16. (?:...)

    import re
ret = re.search("(?:<html>)a(</html>)","aaaaa<html>a</html>")
print(ret.groups())

  17. (?aiLmsux-imsx:...)嵌套与局部删除

    import re
ret = re.search("(?i:(?:a|b)+(?-i:c+))","aaaaaAAAbbbccC")
print(ret)

  18. (?P<name>...) 创建一个命名组

    • 在同一个规则中引用
      	import re
	ret = re.search("(?P<header><html>)a\\1","aaaaa<html>a<html>")
	print(ret,ret.groups())

      	import re
	ret = re.search("(?P<header><html>)a(?P=header)","aaaaa<html>a<html>")
	print(ret,ret.groups())
    • 在结果中访问
      	import re
	ret = re.search("(?P<header><html>)a(?P=header)","aaaaa<html>a<html>")
	print(ret,ret.group("header"))
    • 在subn方法中使用
      	import re
	ret = re.subn("(?P<header><html>)","<\\g<header>>","aaaaa<html>a<html>")
	print(ret)

      	import re
	ret = re.subn("(?P<header><html>)","<\\g<1>>","aaaaa<html>a<html>")
	print(ret)

      	import re
	ret = re.subn("(?P<header><html>)","<\\1>","aaaaa<html>a<html>")
	print(ret)

  19. (?P=name)与前面的相呼应。

  20. (?#...)

    import re
ret = re.search("(?P<header><html>)(?# this is a comment)","aaaaa<html>a<html>")
print(ret,ret.groups())

  21. (?=...)

    import re
ret = re.findall("(?P<header><html>)","aaaaa<html>a<html>")
print(ret)
ret = re.findall("(?P<header><html>(?=$))","aaaaa<html>a<html>")
print(ret)

  22. (?!...)

  23. (?<=...)

    import re
ret = re.findall("(?<=aa|bb)<html>","aaaaa<html>a<html>")
print(ret)

  24. (?<!...)

  25. (?(id/name)yes-pattern|no-pattern)

    import re
ret = re.match("(<html>)(<html>)?(<html>)?a(?(3)</html>|)(?(2)</html>|)(?(1)</html>|$)",
"<html><html>a</html></html>")
print(ret)

    上面的(<html>)?需要与后面的进行搭配。不然会出错。

12-03 02:08
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