re.match 尝试从字符串的起始位置匹配一个模式，如果不是起始位置匹配成功的话，match()就返回none。
使用Python的‘r’前缀，就不用考虑转义的问题了
我们可以使用group(num) 或 groups() 匹配对象函数来获取匹配表达式。
测试用例
#!/usr/bin/python
import re
line = "Cats are smarter than dogs"
matchObj = re.match( r'(.*) are (.*?) (.*)', line, re.M|re.I)
if matchObj:
print "matchObj.group() : ", matchObj.group()
print "matchObj.group(1) : ", matchObj.group(1)
print "matchObj.group(2) : ", matchObj.group(2)
print "matchObj.group(3) : ", matchObj.group(3)
else:
print "No match!!"
python test.py
matchObj.group() : Cats are smarter than dogs
matchObj.group(1) : Cats
matchObj.group(2) : smarter
matchObj.group(3) : than dogs
变形一
matchObj = re.match( r'(.*) are (.*) .*', line, re.M|re.I)
python test.py
matchObj.group() : Cats are smarter than dogs
matchObj.group(1) : Cats
matchObj.group(2) : smarter than
matchObj.group(3) :
Traceback (most recent call last):
File "test.py", line 12, in <module>
print "matchObj.group(3) : ", matchObj.group(3)
IndexError: no such group
你在正则表达式内所看到的，通过括号括起来的group，编号分别对应着1,2,3,少了个（）导致数组越界报错
变形二
matchObj = re.match( r'(.*) are (.*) (.*)', line, re.M|re.I)
python test.py
matchObj.group() : Cats are smarter than dogs
matchObj.group(1) : Cats
matchObj.group(2) : smarter than
matchObj.group(3) : dogs
. 代表任意字符
* 匹配前面的字符或者子表达式0次或多次，因为没有?,所以group2会匹配多次
变形三
matchObj = re.match( r'(.*) (.*?) (.*)', line, re.M|re.I)
python test.py
matchObj.group() : Cats are smarter than dogs
matchObj.group(1) : Cats are smarter
matchObj.group(2) : than
matchObj.group(3) : dogs
. 代表任意字符
* 匹配前面的字符或者子表达式0次或多次
*? 惰性匹配上一个
变形四
matchObj = re.match( r'(.*?) (.*?) (.*)', line, re.M|re.I)
python test.py
matchObj.group() : Cats are smarter than dogs
matchObj.group(1) : Cats
matchObj.group(2) : are
matchObj.group(3) : smarter than dogs
变形五
matchObj = re.match( r'(.*) (.*) (.*)', line, re.M|re.I)
python test.py
matchObj.group() : Cats are smarter than dogs
matchObj.group(1) : Cats are smarter
matchObj.group(2) : than
matchObj.group(3) : dogs
变形六
matchObj = re.match( r'(.*)(.*) (.*)', line, re.M|re.I)
python test.py
matchObj.group() : Cats are smarter than dogs
matchObj.group(1) : Cats are smarter than
matchObj.group(2) :
matchObj.group(3) : dogs
因(.*)(.*)间没有空格，所以group2匹配为空