Python进阶笔记(1):正则表达式

简介: Python进阶笔记(1):正则表达式

正则表达式


需要导入:import re


1. 匹配符


常用普通字符的含义见下表


普通字符 含义
\W 匹配非数字、字母、下划线、汉字
\w 匹配数字、字母、下划线、汉字
\S 匹配任意非空白字符
\s 匹配任意空白字符
\D 匹配非数字
\d 匹配数字


常用元字符的含义见下表


元字符 含义
. 匹配任意字符(除换行符\r,\n)
^ 匹配字符串的开始位置
$ 匹配字符串的结束位置
* 匹配该元字符的前一个字符任意出现次数(包括0次)
匹配该元字符的前一个字符0次或1次
\ 转义字符,其后的一个元字符失去特殊含义,匹配字符本身
() ()中的表达式称为一个组,组匹配到的字符能被取出
[] 字符集,范围内的所有字符都能被匹配
| 将匹配条件进行逻辑或运算
[abc] 匹配括号内任意字符
[^abc] 匹配非括号内任意字符


2. findall()


使用re模块里面的findall()函数进行查找匹配,返回一个列表。


2.1 \w和\W


import re
str1 = '123Qwe!_@#你我他'
print(re.findall('\w', str1))    # 匹配数字、字母、下划线、汉字
print(re.findall('\W', str1))    # 匹配非数字、字母、下划线、汉字


['1', '2', '3', 'Q', 'w', 'e', '_', '你', '我', '他']
['!', '@', '#']


2.2 \s和\S


import re
str2 = "123Qwe!_@#你我他\t \n\r"
print(re.findall('\s', str2))   # 匹配任意空白字符,如空格、换行符\r
print(re.findall('\S', str2))   # 匹配任意非空白字符


['\t', ' ', '\n', '\r']
['1', '2', '3', 'Q', 'w', 'e', '!', '_', '@', '#', '你', '我', '他']


2.3 \d和\D


import re
str3 = "123Qwe!_@#你我他\t \n\r"
print(re.findall('\d', str3))  # 匹配数字
print(re.findall('\D', str3))  # 匹配非数字


['1', '2', '3']
['Q', 'w', 'e', '!', '_', '@', '#', '你', '我', '他', '\t', ' ', '\n', '\r']


2.4 ^和$


import re
str4 = '你好吗,我很好'
print(re.findall('^你好', str4))  # 匹配字符串的开始的 你好
str5 = '我很好,你好'
print(re.findall('你好$', str5))  # 匹配字符串的结束的 你好 


['你好']
['你好']


2.5 . * ?


import re
str6 = 'abcaaabb'
print(re.findall('a.b', str6))  # 匹配任意一个字符(除换行符\r,\n)
print(re.findall('a?b', str6))  # 匹配字符a0次或1次
print(re.findall('a*b', str6))  # 匹配字符a任意次数(包括0次)
print(re.findall('a.*b', str6)) # 匹配任意字符任意次数 (贪婪匹配)    能匹配多长就多长
print(re.findall('a.*?b', str6))# 匹配任意字符任意次数 (非贪婪匹配)  能匹配多短就多短


['aab']
['ab', 'ab', 'b']
['ab', 'aaab', 'b']
['abcaaabb']
['ab', 'aaab']


2.6 \


import re
str7 = '\t123456'
print(re.findall('t', str7))   # 匹配不到字符t,因为\t有特殊含义,是一个先整体
str8 = '\\t123456' 
print(re.findall('t', str8))   # 使用转义字符后,\t变为无特殊含义的普通字符,能匹配到字符t
str9 = r'\t123456'
print(re.findall('t', str9))   # 在字符串前加r也可以对字符串进行转义


[]
['t']
['t']


2.7 []


import re
str10 = 'aab abb acb azb a1b'
print(re.findall('a[a-z]b', str10))   # 只要中间的字符在字母a~z之间就能匹配到
print(re.findall('a[0-9]b', str10))   # 只要中间的字符在数字0~9之间就能匹配到
print(re.findall('a[ac1]b', str10))   # 只要中间的字符是[ac1]的成员就能匹配到


['aab', 'abb', 'acb', 'azb']
['a1b']
['aab', 'acb', 'a1b']


2.8 ()


import re
str11 = '123qwer'
print(re.findall('(\w+)q(\w+)', str11))  # \w+ 代表匹配一个或多个数字、字母、下划线、汉字


[('123', 'wer')]


2.9 |


import re
str12 = '你好,女士们先生们,大家好好学习呀'
print(re.findall('女士|先生', str12))  # 匹配  先生  或 女士


['女士', '先生']


3. search()


3.1 匹配电话


实例:查找电话


def isPhoneNumber(text):
    """查找\d\d\d-\d\d\d-\d\d\d\d类型的电话的函数 非正则版"""
    if len(text) != 12:
        return False
    for i in range(0,3):
        if not text[i].isdecimal():
            return False
    if text[3] != '-':
        return False
    for i in range(4,7):
        if not text[i].isdecimal():
            return False
    if text[7] != '-':
        return False
    for i in range(8,12):
        if not text[i].isdecimal():
            return False
    return True
message = "Call me at 415-555-1011 tomorrow. 415-555-9999 is my office"
for i in range(len(message)):
    chunk = message[i:i+12]
    if isPhoneNumber(chunk):
        print("Phone number found: " + chunk)
print("Done")


Phone number found: 415-555-1011
Phone number found: 415-555-9999
Done


实例:用正则表达式查找电话号


import re
phoneNumRegex = re.compile(r'\d\d\d-\d\d\d-\d\d\d\d')
mo = phoneNumRegex.search("My number is 415-555-4242.")
print("Phone number found: " + mo.group())


Phone number found: 415-555-4242


正则表达式使用步骤总结:


  1. import re导入正则表达式模块


  1. re.compile()函数创建一个Regex对象(记得使用原始字符串)


  1. 向Regex对象的search()方法传入想查找的字符串。它返回一个Match对象


  1. 调用Match对象的group()方法,返回实际匹配文本的字符串


3.2 利用括号分组


import re
phoneNumRegex = re.compile(r'(\d\d\d)-(\d\d\d-\d\d\d\d)')
mo = phoneNumRegex.search("My number is 415-555-4242.")
print(mo.group())
print(mo.group(1)) 
print(mo.group(2))
print(mo.groups())   # 获取所有的分组
areaCode, mainNumber = mo.groups()
print(areaCode, mainNumber)


415-555-4242
415
555-4242
('415', '555-4242')
415 555-4242


3.3 用管道匹配多个分组


字符|称为”管道“,希望匹配许多表达式中的一个,就用它。


第一次出现的匹配文本,将作为Match对象返回。


heroRegex = re.compile(r'Batman|Tina Fey')
mo1 = heroRegex.search('Batman and Tina Fey.')
print(mo1.group())   # 查找第一次出现的   findall()则是查找所有
mo2 = heroRegex.search("Tina Fey and Batman.")
print(mo2.group())


Batman
Tina Fey



batRegex = re.compile(r'Bat(man|mobile|copter|bat)')
mo = batRegex.search('Batmobile lost a wheel')
print(mo.group())
print(mo.group(1))


Batmobile
mobile


3.4 用问号实现可选匹配


batRegex = re.compile(r'Bat(wo)?man')
mo1 = batRegex.search('The Adventures of Batman')
print(mo1.group())
mo2 = batRegex.search('The Adventures of Batwoman')
print(mo2.group())


Batman
Batwoman


例2


phoneRegex = re.compile(r'(\d\d\d-)?\d\d\d-\d\d\d\d')
mo1 = phoneRegex.search('My number is 415-555-4242')
print(mo1.group())
mo2 = phoneRegex.search('My number is 555-4242')
print(mo2.group())


415-555-4242
555-4242


3.5 用星号匹配零次或多次


batRegex = re.compile(r'Bat(wo)*man')
mo1 = batRegex.search('The Adventures of Batman')
print(mo1.group())
mo2 = batRegex.search('The Adventures of Batwoman')
print(mo2.group())
mo3 = batRegex.search('The Adventures of Batwowowowoman')
print(mo3.group())


Batman
Batwoman
Batwowowowoman


3.6 用花括号匹配待定次数


(Ha){3}将匹配字符串HaHaHa
(Ha){3,5}将匹配字符串HaHaHa | HaHaHaHa | HaHaHaHaHa
(Ha){3,}匹配3次及以上
(Ha){,5}匹配0到5次



haRegex = re.compile(r'(Ha){3}')
mo1 = haRegex.search('HaHaHa')
print(mo1.group())
mo2 = haRegex.search('Ha')
print(mo2 == None)  # 因为(Ha){3}匹配HaHaHa,不匹配Ha,所以返回None


HaHaHa
True


3.7 贪心和非贪心匹配


# 贪心
greedyHaRegex = re.compile(r'(Ha){3,5}')
mo1 = greedyHaRegex.search('HaHaHaHaHa')
print(mo1)
# 非贪心
greedyHaRegex = re.compile(r'(Ha){3,5}?')
mo1 = greedyHaRegex.search('HaHaHaHaHa')
print(mo1)


<re.Match object; span=(0, 10), match='HaHaHaHaHa'>
<re.Match object; span=(0, 6), match='HaHaHa'>


3.8 练习


例:search和findall的区别


phoneNumRegex = re.compile(r'\d\d\d-\d\d\d-\d\d\d\d')
mo = phoneNumRegex.search('Cell: 415-555-9999 Work: 212-555-0000')
print(mo.group())
phoneNumRegex = re.compile(r'\d\d\d-\d\d\d-\d\d\d\d')
print(phoneNumRegex.findall('Cell: 415-555-9999 Work: 212-555-0000'))
phoneNumRegex = re.compile(r'(\d\d\d)-(\d\d\d)-(\d\d\d\d)')
print(phoneNumRegex.findall('Cell: 415-555-9999 Work: 212-555-0000'))


415-555-9999
['415-555-9999', '212-555-0000']
[('415', '555', '9999'), ('212', '555', '0000')]


例:匹配元音字符


  • [abc]:匹配括号内任意字符


  • [^abc]:匹配不再括号内的任意字符


# 匹配所有元音字符
voweRgegx = re.compile(r'[aeiouAEIOU]')
print(voweRgegx.findall('RoboCop eats baby food. BABY FOOD.'))
# 匹配所有非元音字符
consonantRgegx = re.compile(r'[^aeiouAEIOU]')
print(consonantRgegx.findall('RoboCop eats baby food. BABY FOOD.'))


例:插入字符


beginWithHello = re.compile(r'^Hello')
print(beginWithHello.search('Hello world!'))
print(beginWithHello.search('He said hello.') == None)


<re.Match object; span=(0, 5), match='Hello'>
True


例:美元字符


endWithNumber = re.compile(r'\d$')
print(endWithNumber.search('Your number is 42'))
print(endWithNumber.search("Your number is forty two") == None)


<re.Match object; span=(16, 17), match='2'>
True


例:匹配以字符开始字符结束的


wholeStringIsNum = re.compile(r'^\d+$')
print(wholeStringIsNum.search('123456789'))
print(wholeStringIsNum.search('12345xyz678') == None)
print(wholeStringIsNum.search('123 456789') == None)


<re.Match object; span=(0, 9), match='123456789'>
True
True


例:通配字符


atRegex = re.compile(r'.at')
print(atRegex.findall('The cat in the hat sat on the flat mat.'))


['cat', 'hat', 'sat', 'lat', 'mat']


例:用点-星匹配所有字符


nameRegex = re.compile(r'First Name: (.*) Last Name: (.*)')
mo = nameRegex.search("First Name: A1 Last Name: Sweigart")
print(mo.group(1))
print(mo.group(2))


A1
Sweigart


例:点-星的贪心和非贪心模式


# 非贪心
nongreedyRegex = re.compile(r'<.*?>')
print(nongreedyRegex.search('<To serve man> for dinner.>'))
# 贪心
greedyRegex = re.compile(r'<.*>')
print(greedyRegex.search('<To serve man> for dinner.>'))


<re.Match object; span=(0, 14), match='<To serve man>'>
<re.Match object; span=(0, 27), match='<To serve man> for dinner.>'>


例:用句点字符匹配换行


# 正常情况不匹配换行符
noNewlineRegex = re.compile('.*')
print(noNewlineRegex.search("Serve the public trust.\nProtect the innocent.\nUphold the law.").group())
# 添加第二个参数,匹配换行符
NewlineRegex = re.compile('.*', re.DOTALL)
print(NewlineRegex.search("aaa.\nbbb.").group())


Serve the public trust.
aaa.
bbb.


例:匹配不区分大小写


# 传入第二个参数,匹配不区分大小写
robocop = re.compile(r'robocop', re.I)
print(robocop.search('RoboCop is part manchine, all cop.').group())
print(robocop.search('ROBOcop is part manchine, all cop.').group())


RoboCop
ROBOcop


例:用sub()方法替换字符串


namesRegex = re.compile(r'Agent \w+')
print(namesRegex.sub("CENSORED", "Agent Alice gave the secret documents to Agent Bob."))


CENSORED gave the secret documents to CENSORED.


agentNamesRegex = re.compile(r'Agent (\w)\w*')
print(agentNamesRegex.sub(r'\1****', "Agent Alice told Agent Carol that Agent Eve knew Agent Bob was a double agent."))


A**** told C**** that E**** knew B**** was a double agent.


3.9 实践:匹配电话号码和E-mail地址


import pyperclip, re
phoneRegex = re.compile(r'''(
        (\d{3}|\(\d{3}\))?
        (\s|-|\.)?
        (\d{3})
        (\s|-|\.)
        (\d{4})
        (\s*(ext|x|ext\.)\s*(\d{2,5}))?
        )''', re.VERBOSE)
emailRegex = re.compile(r'''(
        [a-zA-Z0-9._%=-]+
        @
        [a-zA-Z0-9.-]+
        (\.[a-zA-Z]{2,4})
        )''', re.VERBOSE)
text = str(pyperclip.paste())   # 读取剪切板
matches = []
for groups in phoneRegex.findall(text):
    phoneNum = '-'.join([groups[1], groups[3], groups[5]])  # 拼接电话
    if groups[8] != '':
        phoneNum += ' x' + groups[8]
    matches.append(phoneNum)
for groups in emailRegex.findall(text):
    matches.append(groups[0])
if len(matches) > 0:
    pyperclip.copy('\n'.join(matches))
    print('找到以下电话号码和电子邮箱::')
    print('\n'.join(matches))
else:
    print("未发现电话号码和电子邮箱!")


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