Python 6th Day

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正则表达式

元字符 (metacharacters)

. ^ $ * + ? { } [ ] \ | ( )

[], 用来指定一个字符集（character class），字符集可以单个列出或者指定一个范围，For example,

[abc] will match any of the characters a, b, or c; this is the same as [a-c], which uses a range to express the same set of characters. If you wanted to match only lowercase letters, your RE would be [a-z]

在 [] 中，元字符不起特殊作用，For example, [akm$] will match any of the characters ‘a‘, ‘k‘, ‘m‘, or ‘$‘; ‘$‘ is usually a metacharacter, but inside a character class it’s stripped of its special nature

在 [] 中使用 ‘^‘ 可以表示取非，For example, [^5] will match any character except ‘5‘

使用 \ (backslash) 转义，if you need to match a [ or \, you can precede them with a backslash to remove their special meaning: \[ or \\

predefined sets of characters:

\d == [0-9]
\D == [^0-9]
\s == [ \t\n\r\f\v] # 所有的空格字符
\S == [^ \t\n\r\f\v] # 所有的非空字符
\w == [a-zA-Z0-9_]
\W == [^a-zA-Z0-9_]

字符集可以嵌套使用，For example, [\s,.] is a character class that will match any whitespace character, or ‘,‘ or ‘.‘

‘.‘ matches anything except a newline character

‘*‘ it specifies that the previous character can be matched zero or more times

‘+‘ which matches one or more times

‘?‘ matches either once or zero times, For example, home-?brew matches either homebrew or home-brew

Compiling Regular Expressions

正则表达式被编译成模式对象（pattern objects），模式对象可以用很多种方法进行匹配或者操作。

>>> import re
>>> p = re.compile(‘ab*‘)
>>> p  
<_sre.SRE_Pattern object at 0x...>

使用原生字符串（raw string notation: r）

Python 6th Day

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原文地址：http://www.cnblogs.com/garyang/p/5591792.html