A. Regular Expressions
1.1 Regular expressions and relations re module
Python regular expression is not unique, it is an independent technology, can be used in all programming languages, but use regular expressions in python need to use the re module
1.2 Regular Expressions role and fields of use
Regular expressions are used to filter specific content of the string, as if to match the specific content, you can write directly to the full story, you do not need to write regular
Regular expressions are now generally used in the field of reptiles and data analysis
1.3 character set
Character Group: [character set] in a variety of characters may appear in the same position to form a group of characters in the regular expression with [] indicate characters divided into many categories, such as numbers, letters, punctuation, and so on. If you now ask for a location " only a number appears " , then the characters on this position is only one of the 10 number 0,1,2 ... 9.
ps: In the group of characters between the expression is or relationship as [0-9a-z] indicates that the bit is a digital or lowercase
1.4 Character
1.5 quantifier
ps: quantifier must be more of the later symbol as n * represented as taking any character except newline and the number of try to get to the biggest reason regular on match default is. greedy match (try to match more), to address this date can be added later asked quantifier?, such as + ? , so greedy match will be converted into inert match .
*? 重复任意次，但尽可能少重复 +? 重复1次或更多次，但尽可能少重复 ?? 重复0次或1次，但尽可能少重复 {n,m}? 重复n到m次，但尽可能少重复 {n,}? 重复n次以上，但尽可能少重复
身份证号码是一个长度为15或18个字符的字符串，如果是15位则全部由数字组成，首位不能为0；如果是18位，则前17位全部是数字，末位可能是数字或x res = ('^[1-9]\d{16}[0-9x]|^[1-9]\d{14}')
二.re模块
re模块:在使用re模块中主要使用三种功能:findall,search,match
2.1:findall
基本句式: findall('正则表达式','带匹配的字符串')
res1 = re.findall('[a-z]+','zhang LOVE who is a probleam') res2 = re.findall('[a-z]+','zhAng LOVE who is a proBleam') print(res1) # ['zhang', 'who', 'is', 'a', 'probleam'] print(res2) # ['zh', 'ng', 'who', 'is', 'a', 'pro', 'leam'] # 找出字符串中符合正则表达式全部内容 并且返回的是一个列表,列表中的元素就是正则匹配到的结果
ret1 = re.findall('www.(baidu|oldboy).com', 'www.oldboy.com') ret2 = re.findall('www.(?:baidu|oldboy).com', 'www.oldboy.com') # 忽略分组优先的机制 print(ret1) # ['oldboy'] 这是因为findall会优先把匹配结果组里内容返回,如果想要匹配结果,取消权限即可 print(ret2) # ['www.oldboy.com'] 可以用?:来取消权限
2.2search
search基本句式:search('正则表达式','带匹配的字符串')
res1 = re.search('a','zhang LOVE who is a probleam') print(res1) # search不会给你直接返回匹配到的结果 而是给你返回一个对象 <_sre.SRE_Match object; span=(2, 3), match='a'>
if res1:
print(res1.group()) # a
res1 = re.search('k','zhang LOVE who is a probleam') print(res1) # None if res1: print(res1.group())
ps:1.search只会依据正则表达式查一次,只要找到一个结果就不会往后找了
2.当查找的结果存在返回的是一个对象,需要调用group才能才看
3.当检查的结果不存在返回的值是None,当调用group时会报错,所以在使用时采用if判断,若果返回值为真则调用group取解析
2.3match
res = re.match('z','zhang LOVE who is a probleam') print(res) # search不会给你直接返回匹配到的结果 而是给你返回一个对象 <_sre.SRE_Match object; span=(0, 1), match='z'>
if res:
print(res.group()) # z
ps:match只会匹配字符串开始的部分,若没有符合的返回的值也是None,调用group会报错
2.4其余功能指令
split:
ret = re.split('[ad]', 'abcd') # 先按'a'分割得到''和'bcd',在对''和'bcd'分别按'd'分割 print(ret) # ['', 'bc', ''] 返回的还是列表
ret=re.split("\d+","zhang9929zhang66wang") print(ret) # 结果 ：['zhang', 'zhang', 'wang'] ret1=re.split("(\d+)","zhang9929zhang66wang") print(ret1) # 结果 ： ['zhang', '9929', 'zhang', '66', 'wang']
sub命令:sub('正则表达式','新的内容','待替换的字符串',n)
ret = re.sub('\d', ' love ', 'zhang9zhang2zhang9',1) # 将数字替换成'H'，参数1表示只替换1个 print(ret) # zhang love zhang2zhang9
ps:subn命令的应用
ret = re.subn('\d', ' love ', 'zhang9zhang2zhang9') # 将数字替换成' love '，返回元组(替换的结果,替换了多少次) ret1 = re.subn('\d', ' love ', 'zhang9zhang2zhang9',1) # 将数字替换成' love '，返回元组(替换的结果,替换了多少次) print(ret) # ('zhang love zhang love zhang love ', 3)返回的是一个元组 元组的第二个元素代表的是替换的个数 print(ret1) # ('zhang love zhang2zhang9', 1)
compile命令:将正则表达式编译成一个正则表达式对象
obj = re.compile('\d{3}') #将正则表达式编译成为一个 正则表达式对象，规则要匹配的是3个数字 ret = obj.search('abc123eeee') #正则表达式对象调用search，参数为待匹配的字符串 res1 = obj.findall('347982734729349827384') print(ret.group()) #结果 ： 123 print(res1) #结果 ： ['347', '982', '734', '729', '349', '827', '384']
finditer:返回一个存放匹配结果的迭代器
ret = re.finditer('\d', '43asds54') #finditer返回一个存放匹配结果的迭代器 print(ret) # <callable_iterator object at 0x000001A35617B2B0> print(next(ret).group()) # 等价于ret.__next__() # 4 print(next(ret).group()) # 等价于ret.__next__() # 3 print(next(ret).group()) # 等价于ret.__next__() # 5 print(next(ret).group()) # 等价于ret.__next__() # 4 print(next(ret).group()) # 等价于ret.__next__() 超出迭代取值的范围 直接报错
?P:为正则表达式取别名
res = re.search('^[1-9](?P<password>\d{14})(?P<username>\d{2}[0-9x])?$','110105199812067023') print(res.group()) # 110105199812067023 print(res.group('password')) # 10105199812067 print(res.group(1)) # 10105199812067 print(res.group('username')) # 023 print(res.group(2)) # 023
ps:在取完别名后,由于采用的是searc方法,调用group,可以指定名字的顺序来读取内容(从开始)