Python之re正则模块二

13、编译的标志

可以用re.I、re.M等参数，也可以直接在表达式中添加"?(iLmsux)"标志

*s:单行，“.”匹配包括换行符在内的所有字符

*i：忽略大小写

*L：让"\w"能匹配当地字符，貌似对中文支持不好

*m：多行

*x：忽略多余的空白字符，让表达式更易阅读

*u：Unicode

例子：

>>> re.findall(r"[a-z]+","%123Abc%45xyz&")
['bc', 'xyz']
>>> re.findall(r"[a-z]+","%123Abc%45xyz&",re.I)
['Abc', 'xyz']
>>>
>>> re.findall(r"(?i)[a-z]+","%123Abc%45xyz&",re.I)
['Abc', 'xyz']

更好的格式：

>>> pattern=r"""
...     (\d+) #number
...     ([a-z]+) #letter
... """
>>>
>>> re.findall(pattern,"%123Abc\n%45xyz&",re.i | re.S |re.x)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'i'
#由错误可见是大写
>>> re.findall(pattern,"%123Abc\n%45xyz&",re.I | re.S |re.X)
[('', 'Abc'), ('', 'xyz')]
>>> 

组操作

命名组：(?P<name>...)

>>> for m in re.finditer(r"(?P<digit>(\d+))(?P<letter>([a-z]+))","%123Abc%45xyz&",re.I):
...     print m.groupdict()
...
{'digit': '', 'letter': 'Abc'}
{'digit': '', 'letter': 'xyz'}

无捕获组:(?:...)，作为匹配条件，但不返回：

>>> for m in re.finditer(r"(?:(\d+))(?P<letter>([a-z]+))","%123Abc%45xyz&",re.I):
...     print m.groupdict()
...
{'letter': 'Abc'}
{'letter': 'xyz'}

反向引用:\<number>或者(?P=name),引用前面的组：

>>> for m in re.finditer(r"<(\w)>\w+</(\1)>","%<a>123Abc</a>%<b>45xyz</b>&%"):
...     print m.group()
...
<a>123Abc</a>
<b>45xyz</b>

>>> for m in re.finditer(r"<(?P<tag>\w)>\w+</(?P=tag)>","%<a>123Abc</a>%<b>45xyz</b>&%"):
...     print m.group()
...
<a>123Abc</a>
<b>45xyz</b>

正声明(?=...)：组内容必须出现在右侧，不返回

负声明(?!...)：组内容不能出现在右侧，不返回

反向正声明(?<=):组内容必须出现在左侧，不返回

反向负声明(?<!):组内容不能出现左侧，不返回

>>> for m in re.finditer(r"\d+(?=[ab])","%123Abc%45xyz%780b&",re.I):
...     print m.group()
...
123
780

>>> for m in re.finditer(r"(?<!\d)[a-z]{3,}","%123Abc%45xyz%bysc&",re.I):
...     print m.group()
...
bysc

修改

split：用pattern做分割符切割字符串。如果用“(pattern)”,那么分隔符也会返回。

>>> re.split(r"\W","abc,123,x")
['abc', '', 'x']
>>> re.split(r"(\W)","abc,123,x")
['abc', ',', '', ',', 'x']
#将pattern使用括号引用起来，也返回分隔符

split(pattern, string, maxsplit=0)
    Split the source string by the occurrences of the pattern,
    returning a list containing the resulting substrings.

sub：替换子串，可指定替换次数：

>>> re.split(r"(\W)","abc,123,x")
['abc', ',', '', ',', 'x']
>>> re.sub(r"[a-z]+","*","abc,123,x")
'*,123,*'
>>>
>>> re.sub(r"[a-z]+","*","abc,123,x",1)
'*,123,x'

sub(pattern, repl, string, count=0)
    Return the string obtained by replacing the leftmost
    non-overlapping occurrences of the pattern in string by the
    replacement repl.  repl can be either a string or a callable;
    if a string, backslash escapes in it are processed.  If it is
    a callable, it's passed the match object and must return
    a replacement string to be used.

subn()和sub()差不多，不过返回"(新字符串，替换次数)"：

>>> re.subn(r"\W","*","abc,123,x")
('abc*123*x', 2)

还可以将替换字符串改成函数，以便替换成不同的结果：

>>> def repl(m):
...     print m.group()
...     return "*" *len(m.group())
...
>>> re.subn(r"[a-z]+",repl,"abc,123,x")
abc
x
('***,123,*', 2)
>>>