python正则--group

group作用：
python正则中，用group函数来定位括号表达式匹配到的结果中特定的字段，你可以理解为索引，有n个括号表达式group里面的索引最大值就是n,group(k)就代表第k个括号表达式匹配到的结果，group()/group(1)，打印出所有的匹配结果

.* 代表匹配除换行符之外的所有字符
.*? 后面多个问号，代表非贪婪模式，也就是说只匹配符合条件的最少字符

如果不使用括号表达式，那么只能使用group()/group(1)，打印出所有的匹配结果，而不能使用group(k)

import re

line = "some cats are smarter than dogs are true"
mat1 = re.match(r".* are", line)
mat2 = re.match(r".*? are", line)

print(mat1)
print(mat2)
print(mat1.group(0))
# <re.Match object; span=(0, 35), match='some cats are smarter than dogs are'>
# <re.Match object; span=(0, 13), match='some cats are'>
# some cats are smarter than dogs are

加上索引则会报错：

print(mat1.group(1))
# IndexError: no such group

使用括号表达式，根据索引获取匹配结果：

import re

line = "some cats are smarter than dogs are true"
mat1 = re.match(r"(.*) are", line)
mat2 = re.match(r"(.*?) are .* dogs (.*)", line)

print(mat1.group(1))
print(mat2)
print(mat2.group(1))
print(mat2.group(2))


# some cats are smarter than dogs
# <re.Match object; span=(0, 40), match='some cats are smarter than dogs are true'>
# some cats
# are true

group()一次可以跟多个索引，会生成一个元组

print(type(mat2.group(2, 1)))
# ('are true', 'some cats')
# <class 'tuple'>

groups()则是把所有的group()生成一个元组

print(mat2.groups())
print(type(mat2.groups()))

# ('some cats', 'are true')
# <class 'tuple'>

如果没有括号表达式，直接使用groups()则会得到一个空的元组

import re

line = "some cats are smarter than dogs are true"
mat1 = re.match(r".* are", line)
print(mat1.groups())
# ()