正则表达式之优美匹配，视前匹配，视后匹配 （?x）(?=) (?=)

接着昨天的内容今天探讨，优美匹配和视前和视后匹配

1.格式化匹配

import re

reg = r'''(?x)(\d{4})?  #匹配前四个 支持注释        
            (-)?
            (\d{8})
'''
num = '0571-88982571, 0572-05975867,057269781578, 0539-66862954, 56788888'
pat = re.findall(reg, num)
#print(pat)

for each in pat:
    print(''.join(each))#连接

>>>

0571-88982571
0572-05975867
057269781578
0539-66862954
56788888

2.视前匹配 查找匹配项，但匹配项不显示在结果中，而是返回（？=）前面的匹配项

import re

reg = r'.+(?= ming lili)'
s = ''' hello ming lili python
 welcome to home ming lili java
 hello python
 xxio
'''
pat = re.findall(reg, s)
print(pat)

>>>

[' hello', ' welcome to home']

3.视后匹配 没搞明白，上个例子

import re 
reg = r'\s+(?!ming|lily)(\w+)'
s ='''
    sales@hello.com
    ming@qq.com
    python@wexin.com
    lily@hello.com
   '''
pat = re.findall(reg, s)
print(pat)
>>>

['\nhello', 'world', 'welcome', 'to', 'home ']