正则表达式就是描述字符串排列的一套规则。通常被用来检索、替换那些符合某个模式(规则)的文本。 为什么要学习正则表达式呢，因为我们在爬取数据的时候需要根据我们想要获取的内容来进行爬取，而正则表达式就具有这个基本功能。 在python中，一般我们会使用re模块来实现Python正则表达式的功能。

re常用函数解析：

练习：

import reprint(re.match("www","www.baidu.com").span())print(re.match("www","wwwbaidu.com"))print(re.match("www","ww.baidu.com"))print(re.match("www","baidu.wwwcom"))print(re.match("www","wWw.wwwcom",flags=re.I))#扫描字符串，返回从头起手位置成功的匹配

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练习：

import reprint(re.search("sunck","good man is sunck!sunck is nice"))print(re.search("sunck","good man is Sunck!sunck is nice"))print(re.search("sunck","good man is Sunck!sunck is nice",flags=re.I))

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import reprint(re.findall("sunck","good man is sunck!Sunck is nice",flags=re.I))

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正则表达式元字符: 正则表达式中： 在字符串前加上 r 这个前缀来避免部分疑惑，因为 r 开头的 python字符串是 raw 字符串，所以里面的所有字符都不会被转义 。 一般正则表达式使用反斜杆（\）来转义特殊字符，使其可以匹配字符本身，而不是指定其他特殊的含义。

练习：

import reprint(re.search(".","sunck is a good man 7"))print(re.findall("[^0-9a-zA-Z_]","sunck is a good man 7"))print(re.search("\d","sunck is a good man 7"))print(re.search("[^\d]","sunck is a good man 7"))print(re.findall("[\W]","sunck is a good man 7 "))print(re.findall("[
]","sunck is a good man 7 
"))print(re.findall(".","sunck is a good man 7 
",flags=re.S))    

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锚字符：

练习：

import reprint(re.search("^sunck","sunck is good man")) print(re.search("man#34;,"sunck is good man"))#re.M 多行匹配print(re.findall("^sunck","sunck is good man
sunck is good man",re.M))print(re.search("\Asunck","sunck is good man
sunck is good man",re.M))print(re.findall("man#34;,"sunck is good man
sunck is good man",re.M)) print(re.search("man\Z","sunck is good man
sunck is good man",re.M))

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匹配多个字符

练习：

import reprint(re.findall(r"a?","aaa"))      #非贪婪匹配print(re.findall(r"a*","aaa"))    #贪婪匹配print(re.findall(r".*","aaabaa"))   #贪婪匹配print(re.findall(r"a+","aabaaaa")) #贪婪匹配print(re.findall(r"a+","aba"))print(re.findall(r"a{3}","aaaaabaaaaaa"))

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特殊：

import reprint(re.findall(r"//*.*/*/",    "/* part1  */   /*    part  */")) //*    后面的/是转义特殊字符print(re.findall(r"//*.*?/*/",    "/* part1  */   /*    part  */"))

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re模块深入：

str3="sunck is a good man!sunck is a nice man!sunck is a handsome man"d=re.finditer(r"(sunck)",str3)while True:    try:        i=next(d)        print(d)    except StopIteration as e:        break

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字符串的替换和修改：

str5="sunck is a good good good man!" print(re.sub(r"(good)","nice",str5))print(type(re.sub(r"(good)","nice",str5,count=2)))print(re.subn(r"(good)","nice",str5))print(type(re.subn(r"(good)","nice",str5)))

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分组：

str6="010-53247654"m=re.match(r"(\d{3})-(\d{8})",str6)#使用序号获取对应组的信息，group(0)代表原始字符串print(m.group(0))print(m.group(1))print(m.group(2))print(m.groups())m1=re.match(r"((\d{3})-(\d{8}))",str6)print(m1.group(0))print(m1.group(1))print(m1.group(2))print(m1.group(3))print(m1.groups())m2=re.match(r"(?P\d{3})-(?P(\d{8}))",str6)print(m2.group("zz"))print(m2.group("ss"))

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编译：

compile(pattern,flags=0)pattern:要编译的正则表达式pat=r"^1(([3578]\d)|(47))\d{8}#34;print(re.match(pat,"13600000000"))#编译成正则对象re_telephon=re.compile(pat)print(re_telephon.match("13600000000"))#re模块调用        re.match(pattern,string,flags=0)#re对象调用        re_telephon.match(string)#re模块调用    re.finditer(pattern,string,flags=0) #re对象调用    re_telephon.finditer(string)#re模块调用re.split(pattern,string=,maxsplit=,flags=0)#re对象调用re_telephon.split(string=,maxsplit=)#re.sub(pattern=,repl=,string=,count=,flags=)#re_telephon.sub(repl=,string=,count=)

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正则表达式实例练习：

总结： 在学完了正则表达式之后，我们需要多加练习。 有了一定的掌握就可以进入实战状态了。