python中的正则表达式

「爱情、让人受尽委屈。」 2022-06-05 06:55 226阅读 0赞

# [python中的正则表达式（re模块）][python_re] #

## 一、简介 ##

正则表达式本身是一种小型的、高度专业化的编程语言，而在python中，通过内嵌集成re模块，程序媛们可以直接调用来实现正则匹配。正则表达式模式被编译成一系列的字节码，然后由用C编写的匹配引擎执行。

## 二、正则表达式中常用的字符含义 ##

1、普通字符和11个元字符：

<table style="margin:0px; padding:0px; border-collapse:collapse; border-spacing:0px; border:1px solid silver; word-break:break-word; height:266px; width:549px"> 
 <tbody style="margin:0px; padding:0px"> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 普通字符</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      匹配自身 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      abc 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      abc 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      . 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 匹配任意除换行符"\n"外的字符(在DOTALL模式中也能匹配换行符</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      a.c 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      abc 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      \ 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      转义字符，使后一个字符改变原来的意思 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      a\.c;a\\c 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      a.c;a\c 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      * 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      匹配前一个字符0或多次 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      abc* 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      ab;abccc 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      + 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      匹配前一个字符1次或无限次 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      abc+ 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      abc;abccc 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      ? 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      匹配一个字符0次或1次 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      abc? 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      ab;abc 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      ^ 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 匹配字符串开头。在多行模式中匹配每一行的开头</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> ^abc</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      abc 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      $ 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 匹配字符串末尾，在多行模式中匹配每一行的末尾</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> abc$</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      abc 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> |</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 或。匹配|左右表达式任意一个，从左到右匹配，如果|没有包括在()中，则它的范围是整个正则表达式</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      abc|def 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      abc 
    </div> 
    <div style="margin:0px; padding:0px">
      def 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> {}</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> {m}匹配前一个字符m次，{m,n}匹配前一个字符m至n次，若省略n，则匹配m至无限次</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      ab{1,2}c 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      abc 
    </div> 
    <div style="margin:0px; padding:0px">
      abbc 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      [] 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 字符集。对应的位置可以是字符集中任意字符。字符集中的字符可以逐个列出，也可以给出范围，如[abc]或[a-c]。[^abc]表示取反，即非abc。<br style="margin:0px; padding:0px"> 所有特殊字符在字符集中都失去其原有的特殊含义。用\反斜杠转义恢复特殊字符的特殊含义。</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      a[bcd]e 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      abe 
    </div> 
    <div style="margin:0px; padding:0px">
      ace 
    </div> 
    <div style="margin:0px; padding:0px">
      ade 
    </div> 
    <div style="margin:0px; padding:0px">
      &nbsp; 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      () 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 被括起来的表达式将作为分组，从表达式左边开始没遇到一个分组的左括号“（”，编号+1.<br style="margin:0px; padding:0px"> 分组表达式作为一个整体，可以后接数量词。表达式中的|仅在该组中有效。</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> (abc){2}<br style="margin:0px; padding:0px"> a(123|456)c</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      abcabc 
    </div> 
    <div style="margin:0px; padding:0px">
      a456c 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

这里需要强调一下反斜杠\\的作用：

*  反斜杠后边跟元字符去除特殊功能；（即将特殊字符转义成普通字符）
 *  反斜杠后边跟普通字符实现特殊功能；（即预定义字符）
 *  引用序号对应的字组所匹配的字符串。

a=re.search(r'(tina)(fei)haha\2','tinafeihahafei tinafeihahatina').group()
    print(a)
    结果：
    tinafeihahafei

2、预定义字符集（可以写在字符集\[...\]中）

<table style="margin:0px; padding:0px; border-collapse:collapse; border-spacing:0px; border:1px solid silver; word-break:break-word; height:212px; width:580px"> 
 <tbody style="margin:0px; padding:0px"> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      \d 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 数字:[0-9]</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      a\bc 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      a1c 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      \D 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 非数字:[^\d]</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      a\Dc 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      abc 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      \s 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 匹配任何空白字符:[&lt;空格&gt;\t\r\n\f\v]</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      a\sc 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      a c 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> \S</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 非空白字符:[^\s]</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      a\Sc 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      abc 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      \w 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 匹配包括下划线在内的任何字字符:[A-Za-z0-9_]</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      a\wc 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      abc 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      \W 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 匹配非字母字符，即匹配特殊字符</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      a\Wc 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      a c 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      \A 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 仅匹配字符串开头,同^</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> \Aabc</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      abc 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      \Z 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 仅匹配字符串结尾，同$</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      abc\Z 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      abc 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      \b 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 匹配\w和\W之间，即匹配单词边界匹配一个单词边界，也就是指单词和空格间的位置。例如， 'er\b' 可以匹配"never" 中的 'er'，但不能匹配 "verb" 中的 'er'。</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> \babc\b<br style="margin:0px; padding:0px"> a\b!bc</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 空格abc空格<br style="margin:0px; padding:0px"> a!bc</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      \B 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> [^\b]</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      a\Bbc 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      abc 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

![复制代码][copycode.gif]

这里需要强调一下\b的单词边界的理解：
    w = re.findall('\btina','tian tinaaaa')
    print(w)
    s = re.findall(r'\btina','tian tinaaaa')
    print(s)
    v = re.findall(r'\btina','tian#tinaaaa')
    print(v)
    a = re.findall(r'\btina\b','tian#tina@aaa')
    print(a)
    执行结果如下：
    []
    ['tina']
    ['tina']
    ['tina']

![复制代码][copycode.gif]

3、特殊分组用法：

<table style="margin:0px; padding:0px; border-collapse:collapse; border-spacing:0px; border:1px solid silver; word-break:break-word; height:88px; width:583px"> 
 <tbody style="margin:0px; padding:0px"> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      (?P&lt;name&gt;) 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 分组，除了原有的编号外再指定一个额外的别名</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> (?P&lt;id&gt;abc){2}</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      abcabc 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      (?P=name) 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 引用别名为&lt;name&gt;的分组匹配到字符串</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> (?P&lt;id&gt;\d)abc(?P=id)</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      1abc1 
    </div> 
    <div style="margin:0px; padding:0px">
      5abc5 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      \&lt;number&gt; 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 引用编号为&lt;number&gt;的分组匹配到字符串</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> (\d)abc\1</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px"> 
     <div style="margin:0px; padding:0px">
       1abc1 
     </div> 
     <div style="margin:0px; padding:0px">
       5abc5 
     </div> 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

## 三、re模块中常用功能函数 ##

1、compile()

编译正则表达式模式，返回一个对象的模式。（可以把那些常用的正则表达式编译成正则表达式对象，这样可以提高一点效率。）

格式：

re.compile(pattern,flags=0)

pattern: 编译时用的表达式字符串。

flags 编译标志位，用于修改正则表达式的匹配方式，如：是否区分大小写，多行匹配等。常用的flags有：

<table style="margin:0px; padding:0px; border-collapse:collapse; border-spacing:0px; border:1px solid silver; word-break:break-word; height:140px; width:601px"> 
 <tbody style="margin:0px; padding:0px"> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 标志</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      含义 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      re.S(DOTALL) 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 使.匹配包括换行在内的所有字符</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      re.I（IGNORECASE） 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      使匹配对大小写不敏感 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      re.L（LOCALE） 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      做本地化识别（locale-aware)匹配，法语等 
     <img alt="" style="margin:0px; padding:0px; border:0px; max-width:900px"> 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      re.M(MULTILINE) 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      多行匹配，影响^和$ 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      re.X(VERBOSE) 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      该标志通过给予更灵活的格式以便将正则表达式写得更易于理解 
    </div> </td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      re.U 
    </div> </td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 
    <div style="margin:0px; padding:0px">
      根据Unicode字符集解析字符，这个标志影响\w,\W,\b,\B 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

![复制代码][copycode.gif]

import re
    tt = "Tina is a good girl, she is cool, clever, and so on..."
    rr = re.compile(r'\w*oo\w*')
    print(rr.findall(tt))   #查找所有包含'oo'的单词
    执行结果如下：
    ['good', 'cool']

![复制代码][copycode.gif]

2、match()

决定RE是否在字符串刚开始的位置匹配。//注：这个方法并不是完全匹配。当pattern结束时若string还有剩余字符，仍然视为成功。想要完全匹配，可以在表达式末尾加上边界匹配符'$'

格式：

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

print(re.match('com','comwww.runcomoob').group())
    print(re.match('com','Comwww.runcomoob',re.I).group())
    执行结果如下：
    com
    com

3、search()

格式：

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

re.search函数会在字符串内查找模式匹配,只要找到第一个匹配然后返回，如果字符串没有匹配，则返回None。

print(re.search('\dcom','www.4comrunoob.5com').group())
    执行结果如下：
    4com

\*注：match和search一旦匹配成功，就是一个match object对象，而match object对象有以下方法：

*  group() 返回被 RE 匹配的字符串
 *  start() 返回匹配开始的位置
 *  end() 返回匹配结束的位置
 *  span() 返回一个元组包含匹配 (开始,结束) 的位置
 *  group() 返回re整体匹配的字符串，可以一次输入多个组号，对应组号匹配的字符串。

a. group（）返回re整体匹配的字符串，  
b. group (n,m) 返回组号为n，m所匹配的字符串，如果组号不存在，则返回indexError异常  
c.groups（）groups() 方法返回一个包含正则表达式中所有小组字符串的元组，从 1 到所含的小组号，通常groups()不需要参数，返回一个元组，元组中的元就是正则表达式中定义的组。

![复制代码][copycode.gif]

import re
    a = "123abc456"
     print(re.search("([0-9]*)([a-z]*)([0-9]*)",a).group(0))   #123abc456,返回整体
     print(re.search("([0-9]*)([a-z]*)([0-9]*)",a).group(1))   #123
     print(re.search("([0-9]*)([a-z]*)([0-9]*)",a).group(2))   #abc
     print(re.search("([0-9]*)([a-z]*)([0-9]*)",a).group(3))   #456
    ###group(1) 列出第一个括号匹配部分，group(2) 列出第二个括号匹配部分，group(3) 列出第三个括号匹配部分。###

![复制代码][copycode.gif]

4、findall()

re.findall遍历匹配，可以获取字符串中所有匹配的字符串，返回一个列表。

格式：

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

p = re.compile(r'\d+')
    print(p.findall('o1n2m3k4'))
    执行结果如下：
    ['1', '2', '3', '4']

![复制代码][copycode.gif]

import re
    tt = "Tina is a good girl, she is cool, clever, and so on..."
    rr = re.compile(r'\w*oo\w*')
    print(rr.findall(tt))
    print(re.findall(r'(\w)*oo(\w)',tt))#()表示子表达式 
    执行结果如下：
    ['good', 'cool']
    [('g', 'd'), ('c', 'l')]

![复制代码][copycode.gif]

5、finditer()

搜索string，返回一个顺序访问每一个匹配结果（Match对象）的迭代器。找到 RE 匹配的所有子串，并把它们作为一个迭代器返回。

格式：

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

![复制代码][copycode.gif]

iter = re.finditer(r'\d+','12 drumm44ers drumming, 11 ... 10 ...')
    for i in iter:
        print(i)
        print(i.group())
        print(i.span())
    执行结果如下：
    <_sre.SRE_Match object; span=(0, 2), match='12'>
    12
    (0, 2)
    <_sre.SRE_Match object; span=(8, 10), match='44'>
    44
    (8, 10)
    <_sre.SRE_Match object; span=(24, 26), match='11'>
    11
    (24, 26)
    <_sre.SRE_Match object; span=(31, 33), match='10'>
    10
    (31, 33)

![复制代码][copycode.gif]

6、split()

按照能够匹配的子串将string分割后返回列表。

可以使用re.split来分割字符串，如：re.split(r'\\s+', text)；将字符串按空格分割成一个单词列表。

格式：

re.split(pattern, string\[, maxsplit\])

maxsplit用于指定最大分割次数，不指定将全部分割。

print(re.split('\d+','one1two2three3four4five5'))
    执行结果如下：
    ['one', 'two', 'three', 'four', 'five', '']

7、sub()

使用re替换string中每一个匹配的子串后返回替换后的字符串。

格式：

re.sub(pattern, repl, string, count)

![复制代码][copycode.gif]

import re
    text = "JGood is a handsome boy, he is cool, clever, and so on..."
    print(re.sub(r'\s+', '-', text))
    执行结果如下：
    JGood-is-a-handsome-boy,-he-is-cool,-clever,-and-so-on...

其中第二个函数是替换后的字符串；本例中为'-'

第四个参数指替换个数。默认为0，表示每个匹配项都替换。

![复制代码][copycode.gif]

re.sub还允许使用函数对匹配项的替换进行复杂的处理。

如：re.sub(r'\\s', lambda m: '\[' + m.group(0) + '\]', text, 0)；将字符串中的空格' '替换为'\[ \]'。

import re
    text = "JGood is a handsome boy, he is cool, clever, and so on..."
    print(re.sub(r'\s+', lambda m:'['+m.group(0)+']', text,0))
    执行结果如下：
    JGood[ ]is[ ]a[ ]handsome[ ]boy,[ ]he[ ]is[ ]cool,[ ]clever,[ ]and[ ]so[ ]on...

8、subn()

返回替换次数

格式：

subn(pattern, repl, string, count=0, flags=0)

![复制代码][copycode.gif]

print(re.subn('[1-2]','A','123456abcdef'))
    print(re.sub("g.t","have",'I get A,  I got B ,I gut C'))
    print(re.subn("g.t","have",'I get A,  I got B ,I gut C'))
    执行结果如下：
    ('AA3456abcdef', 2)
    I have A,  I have B ,I have C
    ('I have A,  I have B ,I have C', 3)

![复制代码][copycode.gif]

## 四、一些注意点 ##

1、re.match与re.search与re.findall的区别：

re.match只匹配字符串的开始，如果字符串开始不符合正则表达式，则匹配失败，函数返回None；而re.search匹配整个字符串，直到找到一个匹配。

![复制代码][copycode.gif]

a=re.search('[\d]',"abc33").group()
    print(a)
    p=re.match('[\d]',"abc33")
    print(p)
    b=re.findall('[\d]',"abc33")
    print(b)
    执行结果：
    3
    None
    ['3', '3']

![复制代码][copycode.gif]

2、贪婪匹配与非贪婪匹配

\*?,+?,??,\{m,n\}? 前面的\*,+,?等都是贪婪匹配，也就是尽可能匹配，后面加?号使其变成惰性匹配

![复制代码][copycode.gif]

a = re.findall(r"a(\d+?)",'a23b')
    print(a)
    b = re.findall(r"a(\d+)",'a23b')
    print(b)
    执行结果：
    ['2']
    ['23']

![复制代码][copycode.gif]

a = re.match('<(.*)>','<H1>title<H1>').group()
    print(a)
    b = re.match('<(.*?)>','<H1>title<H1>').group()
    print(b)
    执行结果：
    <H1>title<H1>
    <H1>

![复制代码][copycode.gif]

a = re.findall(r"a(\d+)b",'a3333b')
    print(a)
    b = re.findall(r"a(\d+?)b",'a3333b')
    print(b)
    执行结果如下：
    ['3333']
    ['3333']
    #######################
    这里需要注意的是如果前后均有限定条件的时候，就不存在什么贪婪模式了，非匹配模式失效。

![复制代码][copycode.gif]

3、用flags时遇到的小坑

print(re.split('a','1A1a2A3',re.I))#输出结果并未能区分大小写
    这是因为re.split(pattern，string，maxsplit,flags)默认是四个参数，当我们传入的三个参数的时候，系统会默认re.I是第三个参数，所以就没起作用。如果想让这里的re.I起作用，写成flags=re.I即可。

## 五、正则的小实践 ##

1、匹配电话号码

p = re.compile(r'\d{3}-\d{6}')
    print(p.findall('010-628888'))

2、匹配IP

re.search(r"(([01]?\d?\d|2[0-4]\d|25[0-5])\.){3}([01]?\d?\d|2[0-4]\d|25[0-5]\.)","192.168.1.1")

[python_re]: http://www.cnblogs.com/tina-python/p/5508402.html
[copycode.gif]: /images/20220605/7dab860b9ded44f7a533fe08aff12d5b.png