python 正則表達式與JSON-正則表達式匹配數字、非數字、字符、非字符、貪婪模式、非貪婪模式、匹配次數指定等

1、正則表達式：目的是為了爬蟲，是爬蟲利器。

正則表達式是用來做字符串匹配的，比如檢測是不是電話、是不是email、是不是ip地址之類的

2、JSON：外部數據交流的主流格式。

3、正則表達式的使用 

re python 內置的模塊，可以進行正則匹配

re.findall(pattern,source)
pattern：正則匹配規則-也叫鄭澤表達式
source：需要查找的目標源

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、正則表達式的應用

• 查數字

• 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']
  
  
  

  用另外一種匹配模式-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

• 查非數字

• 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']
  
  

  用另外一種匹配模式-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']

   

• 正則表達式的羅列 ：https://baike.baidu.com/item/正則表達式/1700215?fr=aladdin，挨個練習是沒有必要的，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']

取范圍操作：-
#coding=utf-8
import re
a = "abc,acc,adc,aec,afc,ahc"
#取出acc,adc,aec,afc(中間字符是c到f范圍的)
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']

• 匹配數字和字母:

• 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']

   

  顯然，是\w是不匹配非字母和數字的，比如“&”符號

• 匹配非單詞非數字字符

  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、換行符號之類的匹配:\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']

   

• 匹配量詞:匹配出python Java php

• 必須三個一組：

  [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個一組：因為最長python 為6 最短PHP為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']

  疑問：為什么3個能匹配 匹配到pyt的時候為什么不終止？
  因為正則表達式的數量詞分為貪婪和非貪婪模式，默認情況下，python 認為是貪婪模式的。
  
  非貪婪模式怎么使用:加個問號

  [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']

   

   

• * ，對*前面的字符'n',匹配0次或者無限次

• 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 沒有n 則是匹配0次，可匹配出來pytho；比如python 1個n 則是匹配1次，可匹配出來python；pythonn  2個n 則是匹配2次，可匹配出來pythonn

• +,對+前面的字符'n' 匹配1次或者無限次

• 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 沒有n 則是匹配0次，可匹配出來pytho；比如python 1個n 則是匹配1次，可匹配出來python；pythonn  2個n 則是匹配1次，可匹配出來python，因為多出來的n，直接被截斷了，不符合匹配模式，所以匹配不出來pythonn 而是匹配出來的是python。也可以理解成?開啟了非貪婪模式

• 如果要開啟非貪婪模式，但是又不想用*，+ 去匹配無限次，而是指定匹配次數的范圍，那么可以這樣

  python{1,2}

  這表示，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']