Python入门（06） -- 正则表达式

1 原子
(1) 普通字符作为原子

 import repattern = "baidu"string = "www.baidu.com"result = re.search(pattern, string)print(result)

打印结果：

 <_sre.SRE_Match object; span=(4, 9), match='baidu'>

(2) 非打印字符作为原子

 import repattern = '\n'string = """www.baidu.com2017-12-16
"""result = re.search(pattern, string)print(result)

打印结果：

 <_sre.SRE_Match object; span=(13, 14), match='\n'>

正则表达式有什么用，(3) 通用字符作为原子表

 import repattern = "\w\dpython\w"string = "abc333python_py"result = re.search(pattern, string)print(result)

打印结果：

 <_sre.SRE_Match object; span=(4, 13), match='33python_'>

说明：

(4) 原子表

import re
string = "abc123pythonp_py"
pattern1 = "\w\dpython[a-z]\w"
pattern2 = "\w\dpython[^a-z]\w"
pattern3 = "\w\dpython[a-z]\W"
result1 = re.search(pattern1, string)
result2 = re.search(pattern2, string)
result3 = re.search(pattern3, string)
print(result1)
print(result2)
print(result3)

打印结果：

 <_sre.SRE_Match object; span=(4, 14), match='23pythonp_'>NoneNone

正则表达式详解？2 元字符
(1) 任意匹配元字符

import re
pattern = "...Python."
string = "ILove123Python_py"
print(re.search(pattern, string))

(2) 边界限定元字符

import re
"""匹配以ILove开始的字符串"""
pattern1 = "^ILove"
"""匹配以Love开始的字符串"""
pattern2 = "^Love"
"""匹配以py结束的字符串"""
pattern3 = "py$"
"""匹配以ny结束的字符串"""
pattern4 = "ny$"
string = "ILove123Python_py"
result1 = re.search(pattern1, string)
result2 = re.search(pattern2, string)
result3 = re.search(pattern3, string)
result4 = re.search(pattern4, string)
print(result1)
print(result2)
print(result3)
print(result4)

打印结果：

<_sre.SRE_Match object; span=(0, 5), match='ILove'>
None
<_sre.SRE_Match object; span=(15, 17), match='py'>
None

(3) 限定符

import re
string = "ILoveAndccccc123Python_py"
pattern1 = "Py.*n"
"""匹配从o后的两个v"""
pattern2 = "dc{2}"
"""匹配从o后的三个v"""
pattern3 = "dc{3}"
"""匹配从o后的最少两个v"""
pattern4 = "dc{2,}"
result1 = re.search(pattern1, string)
result2 = re.search(pattern2, string)
result3 = re.search(pattern3, string)
result4 = re.search(pattern4, string)
print(result1)
print(result2)
print(result3)
print(result4)

打印结果：

<_sre.SRE_Match object; span=(16, 22), match='Python'>
<_sre.SRE_Match object; span=(7, 10), match='dcc'>
<_sre.SRE_Match object; span=(7, 11), match='dccc'>
<_sre.SRE_Match object; span=(7, 13), match='dccccc'>

正则表达式 不包含。(4) 模式选择符

import re
string = "ILoveAndccccc123Python_py"
pattern = "Love|Python"
print(re.search(pattern, string))

打印结果：

<_sre.SRE_Match object; span=(1, 5), match='Love'>

(5) 模式单元符

import re
pattern1 = "(cd){1,}"
pattern2 = "cd{1,}"
string = "abcdcdcdePython_py"
result1 = re.search(pattern1, string)  
result2 = re.search(pattern2, string)
print(result1)
print(result2)

打印结果：

<_sre.SRE_Match object; span=(2, 8), match='cdcdcd'>
<_sre.SRE_Match object; span=(2, 4), match='cd'>

3 模式修正

import re
pattern1 = "python"
pattern2 = "python"
string = "abcdcdcdePython_py"
result1 = re.search(pattern1, string)  
result2 = re.search(pattern2, string, re.I)
print(result1)
print(result2)

正则表达式怎么用，打印结果：

None
<_sre.SRE_Match object; span=(9, 15), match='Python'>

4 贪婪模式和懒惰模式
1) 贪婪模式:尽可能多的匹配, 找到最后一个y为止
2) 懒惰模式:尽可能少的匹配，找到第一个y为止

import re 
pattern1 = "P.*y"   #贪婪模式
pattern2 = "P.*?y"  #懒惰模式
string = "abcdcdcdePython_py"
result1 = re.search(pattern1, string)  
result2 = re.search(pattern2, string)
print(result1)
print(result2)

打印结果：

<_sre.SRE_Match object; span=(9, 18), match='Python_py'>
<_sre.SRE_Match object; span=(9, 11), match='Py'>