python 正则表达式与JSON-正则表达式匹配数字、非数字、字符、非字符、贪婪模式、非贪婪模式、匹配次数指定等

1、正则表达式：目的是为了爬虫，是爬虫利器。

正则表达式是用来做字符串匹配的，比如检测是不是电话、是不是email、是不是ip地址之类的

2、JSON：外部数据交流的主流格式。

3、正则表达式的使用

re python 内置的模块，可以进行正则匹配

re.findall(pattern,source)
pattern：正则匹配规则-也叫郑泽表达式
source：需要查找的目标源

import re
a = "C0C++7Java8C#Python6JavaScript"
res = re.findall("Java",a)
print res
# [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test10.py"
# ['Java', 'Java']

4、正则表达式的应用

• 查数字

• 用概括字符集：\d

  import re
  a = "C0C++7Java8C#Python6JavaScript"
  res = re.findall("\d",a)
  print res
  # Project/python_ToolCodes/test10.py"
  # ['0', '7', '8', '6']
  
  

  用另外一种匹配模式-字符集：[0-9]

  import re
  a = "C0C++7Java8C#Python6JavaScript"
  res = re.findall("[0-9]",a)
  print res
  # Project/python_ToolCodes/test10.py"
  # ['0', '7', '8', '6']

  其中"Java"叫普通字符，"/d" 源字符

• 查非数字

• 用概括字符集：\D

  import re
  a = "C0C++7Java8C#Python6JavaScript"
  res = re.findall("\D",a)
  print res
  # [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test10.py"
  # ['C', 'C', '+', '+', 'J', 'a', 'v', 'a', 'C', '#', 'P', 'y', 't', 'h', 'o', 'n', 'J', 'a', 'v', 'a', 'S', 'c', 'r', 'i', 'p', 't']
  

  用另外一种匹配模式-字符集：[^0-9]

  import re
  a = "C0C++7Java8C#Python6JavaScript"
  res = re.findall("[^0-9]",a)
  print res
  # Project/python_ToolCodes/test10.py"
  # ['C', 'C', '+', '+', 'J', 'a', 'v', 'a', 'C', '#', 'P', 'y', 't', 'h', 'o', 'n', 'J', 'a', 'v', 'a', 'S', 'c', 'r', 'i', 'p', 't']

• 正则表达式的罗列 ：https://baike.baidu.com/item/正则表达式/1700215?fr=aladdin，挨个练习是没有必要的，用到去查即可

4、匹配模式

• 源字符+普通字符混合模式

[]中的或操作
#coding=utf-8
import re
a = "abc,acc,adc,aec,afc,ahc"
#匹配acc和afc
res = re.findall("a[cf]c",a)
print res
# [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test10.py"
# ['acc', 'afc']

取反操作：^
#coding=utf-8
import re
a = "abc,acc,adc,aec,afc,ahc"
#取出非（acc和afc）的字符
res = re.findall("a[^cf]c",a)
print res
# [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test10.py"
# ['abc', 'adc', 'aec', 'ahc']

取范围操作：-
#coding=utf-8
import re
a = "abc,acc,adc,aec,afc,ahc"
#取出acc,adc,aec,afc(中间字符是c到f范围的)
res = re.findall("a[c-f]c",a)
print res

 #[Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test10.py"

 #['acc', 'adc', 'aec', 'afc']

• 匹配数字和字母:

• 概括字符集匹配：\w
  import re
  a = "abc&cba"
  res = re.findall("\w",a)
  print res
  # [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test10.py"
  # ['a', 'b', 'c', 'c', 'b', 'a']

  使用字符集匹配：[A-Za-Z0-9]
  import re
  a = "abc123&cba321"
  res = re.findall("[A-Za-z0-9]",a)
  print res
  # [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test10.py"
  # ['a', 'b', 'c', '1', '2', '3', 'c', 'b', 'a', '3', '2', '1']

  显然，是\w是不匹配非字母和数字的，比如“&”符号

• 匹配非单词非数字字符

  概括字符集：\W
  import re
  a = "abc123&cba321"
  res = re.findall("\W",a)
  print res
  # [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test10.py"
  # ['&']
  

  使用字符集匹配：^A-Za-z0-9

  import re
  a = "abc123&cba321"
  res = re.findall("[^A-Za-z0-9]",a)
  print res
  # [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test10.py"
  # ['&']

• 空格、制表符、换行符号之类的匹配:\s

• import re
  a = "python 111\tjava&67p\nh\rp"
  res = re.findall("\s",a)
  print res
  # [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test10.py"
  # [' ', '\t', '\n', '\r']

• 匹配量词:匹配出python Java php

• 必须三个一组：

  [a-z]{3}

  import re
  a = "python 1111java678php"
  res = re.findall("[a-z]{3}",a)
  print res
  [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test10.py"
  ['pyt', 'hon', 'jav', 'php']
  
  可以3-6个一组：因为最长python 为6 最短PHP为3：

  [a-z]{3,6}
  

  import re
  a = "python 1111java678php"
  res = re.findall("[a-z]{3,6}",a)
  print res
  # [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test10.py"
  # ['python', 'java', 'php']

  疑问：为什么3个能匹配 匹配到pyt的时候为什么不终止？
  因为正则表达式的数量词分为贪婪和非贪婪模式，默认情况下，python 认为是贪婪模式的。
  
  非贪婪模式怎么使用:加个问号

  [a-z]{3,6}?

  import re
  a = "python 1111java678php"
  res = re.findall("[a-z]{3,6}?",a)
  print res
  # [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test10.py"
  # ['pyt', 'hon', 'jav', 'php']

• * ，对*前面的字符'n',匹配0次或者无限次

• import re
  a = "pytho0python1pythonn2"
  res = re.findall("python*",a)
  print res
  
  # [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test10.py"
  # ['pytho', 'python', 'pythonn']

  比如pytho 没有n 则是匹配0次，可匹配出来pytho；比如python 1个n 则是匹配1次，可匹配出来python；pythonn  2个n 则是匹配2次，可匹配出来pythonn

• +,对+前面的字符'n' 匹配1次或者无限次

• import re
  a = "pytho0python1pythonn2"
  res = re.findall("python+",a)
  print res
  
  # [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test10.py"
  # ['python', 'pythonn']

• ?,?前面的字符'n' 匹配0次或者1次

• import re
  a = "pytho0python1pythonn2"
  res = re.findall("python?",a)
  print res
  
  # [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test10.py"
  # ['pytho', 'python', 'python']

  比如pytho 没有n 则是匹配0次，可匹配出来pytho；比如python 1个n 则是匹配1次，可匹配出来python；pythonn  2个n 则是匹配1次，可匹配出来python，因为多出来的n，直接被截断了，不符合匹配模式，所以匹配不出来pythonn 而是匹配出来的是python。也可以理解成?开启了非贪婪模式

• 如果要开启非贪婪模式，但是又不想用*，+ 去匹配无限次，而是指定匹配次数的范围，那么可以这样

  python{1,2}

  这表示，最多匹配2次，最少匹配1次

• import re
  a = "pytho0python1pythonn2"
  res = re.findall("python{1,2}",a)
  print res
  
  # [Running] python -u "/Users/anson/Documents/Project/python_ToolCodes/test10.py"
  # ['python', 'pythonn']