Python正则表达式中的 re.MatchObject.group()函数
re.MatchObject.group()方法默认返回完整匹配的子组或匹配子组的元组，具体取决于参数的数量
Syntax: re.MatchObject.group([group])
Parameter:
- group: (optional) group defaults to zero (meaning that it it will return the complete matched string). Return -1 if group exists but did not contribute to the match.
Return: Complete match by default else one or more matched subgroups depending on the arguments.
IndexError: If the group number passed as argument is negative or greater than the number of groups defined in the match pattern then an IndexError exception will be raised
AttributeError: If a matching pattern is not found then it raise AttributeError.
考虑下面的例子：
示例 1：
从 emailID 打印用户名、公司名和域的程序
Python3
import re
"""We create a re.MatchObject and store it in
match_object variable
the '()' parenthesis are used to define a
specific group"""
match_object = re.match(r'(\w+)@(\w+)\.(\w+)', 'username@geekforgeeks.org')
""" w in above pattern stands for alphabetical character
+ is used to match a consecutive set of characters
satisfying a given condition
so w+ will match a consecutive set of alphabetical characters"""
# for entire match
print(match_object.group())
# also print(match_object.group(0)) can be used
# for the first parenthesized subgroup
print(match_object.group(1))
# for the second parenthesized subgroup
print(match_object.group(2))
# for the third parenthesized subgroup
print(match_object.group(3))
# for a tuple of all matched subgroups
print(match_object.group(1, 2, 3))Python3
import re
"""We create a re.MatchObject and store it in
match_object variable
the '()' parenthesis are used to define a
specific group"""
match_object = re.match(r'(\w+)@(\w+)\.(\w+)', 'username@geekforgeeks.org')
""" w in above pattern stands for alphabetical character
+ is used to match a consecutive set of characters
satisfying a given condition
so w+ will match a consecutive set of alphabetical characters"""
# Following line will raise IndexError exception
print(match_object.group(7))输出：
username@geekforgeeks.org
username
geekforgeeks
org
('username', 'geekforgeeks', 'org')是时候理解上面的程序了。我们使用re.match()方法在给定字符串(' username@geekforgeeks.org ') 中查找匹配项，' w ' 表示我们正在搜索字母字符，' + ' 表示我们正在搜索给定字符串中的连续字母字符。注意使用' () '括号来定义不同的子组，在上面的例子中，我们在匹配模式中有三个子组。我们得到的结果是一个re.MatchObject ，它存储在 match_object 中。
注意：要了解有关正则表达式模式的更多信息，请参阅Python regex
根据传递的参数， group 方法返回不同的字符串，它还返回匹配字符串的元组。
示例 2：
如果我们在方法参数中传递了一个无效的组号，那么我们将得到一个 IndexError 异常。
Python3
import re
"""We create a re.MatchObject and store it in
match_object variable
the '()' parenthesis are used to define a
specific group"""
match_object = re.match(r'(\w+)@(\w+)\.(\w+)', 'username@geekforgeeks.org')
""" w in above pattern stands for alphabetical character
+ is used to match a consecutive set of characters
satisfying a given condition
so w+ will match a consecutive set of alphabetical characters"""
# Following line will raise IndexError exception
print(match_object.group(7))
输出：
Traceback (most recent call last):
File "/home/8da42759204c98da7baa88422a4a74e0.py", line 17, in
print(match_object.group(7))
IndexError: no such group