python正则化

正则化作用

• 在很多文本编辑器里，正则表达式通常被用来检索、替换那些匹配某个模式的文本¹
• 爬虫

举例

• ‘sa{1,3}s’ 代表重复sa1s, sa2s, sa*3s

In [1]: import re
In [3]: key = "saas and sas and saaas"
In [9]: re.findall('sa{1,3}s', key)                                             
Out[9]: ['saas', 'sas', 'saaas']

In [10]: re.findall('sa{1,9}s', key)                                            
Out[10]: ['saas', 'sas', 'saaas']

In [11]: re.findall('sa{1}s', key)                                              
Out[11]: ['sas']

In [12]: re.findall('sa{3}s', key)                                              
Out[12]: ['saaas']

In [13]: re.findall('sa{2}s', key)                                              
Out[13]: ['saas']

• 匹配之间所有

In [23]: re.findall('sa.+saaas', key)                                           
Out[23]: ['saas and sas and saaas']

In [24]: re.findall('sa.+as', key)                                              
Out[24]: ['saas and sas and saaas']

In [25]: re.findall('sa.+an', key)                                              
Out[25]: ['saas and sas an']


In [26]: key = "[email protected]"   
In [27]: re.findall('@.+.', key)                                                
Out[27]: ['@hit.edu.cn']

In [28]: re.findall('@.+\.', key)                                               
Out[28]: ['@hit.edu.']


In [31]: re.findall('@.+?\.', key)                                              
Out[31]: ['@hit.']

[匹配不捕获]²
这里与在python中使用略有区别

In [1]: key = '<br/><a target=_blank href="www.baidu.com">百度一下</a>百度才知道
   ...: '                                                                       

In [2]: import re                                                               

In [3]: re.findall('(?<=(href=")).{1,200}(?=(">))', key)                        
Out[3]: [('href="', '">')]

In [4]: re.findall('(?<=href=").{1,200}(?=">)', key)                            
Out[4]: ['www.baidu.com']

举例

In [25]: key                                                                    
Out[25]: '<annotation>\n\t<folder>02085620</folder>\n\t<filename>n02085620_10621</filename>\n\t<source>\n\t\t<database>ImageNet database</database>\n\t</source>\n\t<size>\n\t\t<width>500</width>\n\t\t<height>298</height>\n\t\t<depth>3</depth>\n\t</size>\n\t<segment>0</segment>\n\t<object>\n\t\t<name>Chihuahua</name>\n\t\t<pose>Unspecified</pose>\n\t\t<truncated>0</truncated>\n\t\t<difficult>0</difficult>\n\t\t<bndbox>\n\t\t\t<xmin>142</xmin>\n\t\t\t<ymin>43</ymin>\n\t\t\t<xmax>335</xmax>\n\t\t\t<ymax>250</ymax>\n\t\t</bndbox>\n\t</object>\n</annotation>'
In [26]: re.findall('(?<=<xmin>)[0-9]+?(?=</xmin>)', key)                       
Out[26]: ['142']


In [27]: xmin = int(re.findall('(?<=<xmin>)[0-9]+?(?=</xmin>)', key)[0]) 
    ...: xmax = int(re.findall('(?<=<xmax>)[0-9]+?(?=</xmax>)', key)[0]) 
    ...: ymin = int(re.findall('(?<=<ymin>)[0-9]+?(?=</ymin>)', key)[0]) 
    ...: ymax = int(re.findall('(?<=<ymax>)[0-9]+?(?=</ymax>)', key)[0])        

In [28]: xmin                                                                   
Out[28]: 142

In [29]: ymin                                                                   
Out[29]: 43

In [30]: xmax                                                                   
Out[30]: 335

In [31]: ymax                                                                   
Out[31]: 250

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1. https://www.cnblogs.com/chuxiuhong/p/5885073.html ↩︎

2. https://blog.csdn.net/z69183787/article/details/81740803 ↩︎