python之re正则简单够用

0.

1.参考

Python正则表达式指南

https://docs.python.org/2/library/re.html

https://docs.python.org/2/howto/regex.html

https://docs.python.org/3/library/re.html

string	re	备注
	re.match(pattern, string, flags=0)	at the start of the string
S.find(sub [,start [,end]]) -> int	re.search(pattern, string, flags=0)	Scan through string looking for a match
S.replace(old, new[, count]) -> string	re.findall(pattern, string, flags=0)	re.finditer

2.分组 m.group()

xx

In [560]: m.group?
Docstring:
group([group1, ...]) -> str or tuple.
Return subgroup(s) of the match by indices or names.
For 0 returns the entire match.
Type:      builtin_function_or_method

In [542]: m=re.search(r'(-{1,2}(gr))','pro---gram-files')

In [543]: m.group()  #自带
Out[543]: '--gr'

In [544]: m.group(0)  #自带，返回整个匹配到的字符串 For 0 returns the entire match. 注意 m.string 是被检索的完整原文。。。
Out[544]: '--gr'

In [545]: m.group(1)
Out[545]: '--gr'

In [546]: m.group(2)
Out[546]: 'gr'

In [547]: m.group(3)  #加的 （ 不满足则报错
---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
<ipython-input-547-71a2c7935517> in <module>()
----> 1 m.group(3)

IndexError: no such group

In [548]: m.group(1,2)  #选择多个分组，返回tuple
Out[548]: ('--gr', 'gr')

In [549]: m.groups()  #选择所有分组
Out[549]: ('--gr', 'gr')

m.groupdict 用于命名分组

In [557]: m.groupdict?
Docstring:
groupdict([default=None]) -> dict.
Return a dictionary containing all the named subgroups of the match,
keyed by the subgroup name. The default argument is used for groups
that did not participate in the match
Type:      builtin_function_or_method

In [558]: m=re.search(r'(-{1,2}(?P<GR>gr))','pro---gram-files')

In [559]: m.groupdict()
Out[559]: {'GR': 'gr'}

3.提取 re.findall()

re.findall(pattern, string, flags=0)

In [97]: text = "He was carefully disguised but captured quickly by police."

In [98]: re.findall(r"\w+ly", text)  #相当于 m.group(0)
Out[98]: ['carefully', 'quickly']

In [99]: re.findall(r"(\w+)ly", text)  #手动加单个括号限定内容，相当于返回 m.group(1)
Out[99]: ['careful', 'quick']

In [100]: re.findall(r"((\w+)(ly))", text)  #多个括号，从左到右数 (，相当于返回 m.groups()
Out[100]: [('carefully', 'careful', 'ly'), ('quickly', 'quick', 'ly')]

In [102]: re.findall(r"((1\w+)(ly))", text)
  Out[102]: []

4.替换 re.sub()

re.sub(pattern, repl, string, count=0, flags=0)

repl 里面的 前向引用 Backreferences, such as \6, are replaced with the substring matched by group 6 in the pattern. 也可以通过 func 实现。

注意 mysql regexp 不支持 \1

https://stackoverflow.com/questions/4122393/negative-backreferences-in-mysql-regexp  提到 unless you can install/use LIB_MYSQLUDF_PREG.

https://stackoverflow.com/questions/7058209/reference-to-groups-in-a-mysql-regex

In [158]: def func(m):
     ...:     return m.group('DEF')+' '+m.group(2)  #别名
     ...:

In [159]: re.sub(r'(?P<DEF>def)\s+([a-z]+)\s*\(\s*\):', func, 'def func(): def f():')
Out[159]: 'def func def f'

In [160]: re.sub(r'(?P<DEF>def)\s+([a-z]+)\s*\(\s*\):', r'\1 \2', 'def func(): def f():')  #不支持 \别名
Out[160]: 'def func def f'

5. Backreferences 前向引用在 pattern

5.1扑克牌找对子

In [204]: re.search(r'(.).*\1','ab123')

In [205]: re.search(r'(.).*\1','ab121')
Out[205]: <_sre.SRE_Match at 0x71ca120>

In [206]: _.group()
Out[206]: ''

5.2连续多个相同

In [207]: re.search(r'.{3}','')  #错误
Out[207]: <_sre.SRE_Match at 0x71b94a8>

In [208]: re.search(r'(.){3}','') #错误
Out[208]: <_sre.SRE_Match at 0x71ca198>

In [209]: re.search(r'(.)\1\1','') #正确

In [210]: re.search(r'(.)\1\1','')
Out[210]: <_sre.SRE_Match at 0x71ca210>

In [211]: re.search(r'(.)\1{2}','')
Out[211]: <_sre.SRE_Match at 0x71ca288>

In [212]: _.group()
Out[212]: ''