正则表达式使用步骤
1. 用import re导入正则表达式
2. 用re.compile()函数创建一个Regex对象
3. 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
4. 调用Match对象的group方法，返回实际匹配文本的字符串
import re
phoneNumRegex = re.compile(r'\d\d\d-\d\d\d-\d\d\d\d')
mo = phoneNumRegex.search('My number is 415-332-9870')
print('Phone number found: '+ mo.group())
创建分组
添加括号将在正则表达式中创建“分组”：(\d\d\d)-(\d\d\d-\d\d\d\d)
然后可以使用group()匹配对象方法，从一个分组获取匹配的文本。向group方法传入0或不传入参数，将返回整个文本，向group方法传入整数1或2，就可以取得匹配文本的不同部分。
group1 = mo.group(1)
group2 = mo.group(2)
print(group1)
print(group2)
一次获得所有的分组，使用groups()方法:
areaCode, mainNumber = mo.groups()
print(areaCode)
print(mainNumber)
不同特殊字符的用法：
“|”希望匹配许多表达式中的一个时，
正则表达式r'Batman|Tina Fey'将匹配Batman或者Tina Fey, 如果它们都出现在被查找的字符串中，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()) # 返回Batman
mo2 = heroRegex.search("Tina Fey and Batman")
print(mo2.group()) # 返回Tina Fey
"|"中的括号分组使用
batRegex = re.compile(r'Bat(man|mobile|copter|bat)')
mo = batRegex.search("Batmobile lost a wheel.")
print(mo.group(1)) # 匹配括号中出现的第一个字符
print(mo.group()) # 匹配整个对应字符
"?"实现可选匹配，匹配这个问号之前的分组零次或一次
batRegex = re.compile(r'Bat(wo)?man')
mo1 = batRegex.search("The adventures of Batman.")
mo2 = batRegex.search("The adventures of Batwoman.")
print(mo1.group()) # 返回Batman
print(mo2.group()) # 返回Batwoman
"*"实现匹配零次或多次
batRegex = re.compile(r'Bat(wo)*man')
mo1 = batRegex.search("The adventures of Batman.")
mo2 = batRegex.search("The adventures of Batwowowowoman.")
mo3 = batRegex.search("The adventures of Batwoman.")
print(mo1.group())
print(mo2.group())
print(mo3.group())
“+”匹配一次或多次
batRegex = re.compile(r'Bat(wo)+man')
mo1 = batRegex.search("The adventures of Batman.")
mo2 = batRegex.search("The adventures of Batwowowowoman.")
mo3 = batRegex.search("The adventures of Batwoman.")
print(mo1 == None) # 返回True 没有匹配结果
print(mo2.group())
print(mo3.group())
“{n}”匹配出现的次数
haRegex = re.compile(r'(Ha){3}')
mo1 = haRegex.search('HaHaHa')
print(mo1.group())
mo2 = haRegex.search('Ha')
print(mo2 == None)
贪心和非贪心匹配
在次数后面加上?表示非贪心匹配，如{3,5}?则只匹配3次。
greedyHaRegex = re.compile(r'(Ha){3,5}')
nongreedyHaRegex = re.compile(r'(Ha){3,5}?')
mo1 = greedyHaRegex.search('HaHaHaHaHa')
print(mo1.group())
mo2 = nongreedyHaRegex.search('HaHaHaHaHa')
print(mo2.group())
findall()方法
1. 如果调用在一个没有分组的正则表达式上，findall()将返回一个匹配字符串的列表
2. 如果调用在一个有分组的正则表达式上，findall()将返回一个字符串的元组列表
phoneNumRegex = re.compile(r'\d\d\d-\d\d\d-\d\d\d\d')
number_str = "Cell:415-555-9999 Work:212-555-0000"
mo = phoneNumRegex.findall(number_str)
print(mo)
phoneNumRegex = re.compile(r'(\d\d\d)-(\d\d\d)-(\d\d\d\d)')
number_str = "Cell:415-555-9999 Work:212-555-0000"
mo1 = phoneNumRegex.findall(number_str)
print(mo1)
开始和结束匹配
# ^ and $
beginsWithHello = re.compile(r'^Hello')
mo = beginsWithHello.search("Hello World")
print(mo.group())
endWithNumber = re.compile(r'\d$')
mo1 = endWithNumber.search("Your age is 23")
print(mo1.group())
.*匹配所有字符
nameRegex = re.compile(r'First Name: (.*) Last Name: (.*)')
mo2 = nameRegex.search("First Name: Al Last Name: Sweigart")
print(mo2.group())
re.I传入compile第二个参数，忽略大小写
robocop = re.compile(r'robocop',re.I)
mo3 = robocop.search('RoBocop is part man, part machine, all cop')
mo4 = robocop.search('ROBOCOP is part man, part machine')
print(mo3.group())
print(mo4.group())
sub()方法
namesRegex = re.compile(r'Agent \w+')
mo5 = namesRegex.sub('CENSORED','Agent Alice gave the secret to Agent Bob.')
print(mo5)
agentNamesRegex = re.compile(r'Agent (\w)(\w*)')
mo6 = agentNamesRegex.sub(r'*\2','Agent Alice told Agent Carol that Agent Eve knew Agent Bob was a double agent.')
print(mo6)
