re.finditer合并正则提取host与user_name无输出问题求助

单独使用正则提取host或user_name时，代码运行正常并返回正确结果；但将两个正则表达式合并后，使用re.finditer遍历却无法得到任何输出，预期应得到与单独提取一致的结果。

相关代码 #

import re

host = "(?P<host>[\d]{1,3}[.][\d]{1,3}[.][\d]{1,3}[.][\d]{1,3})(?= - )"
user_name = " (?P<user_name>((?<= - )[a-zA-Z]+[\d]+)|((?<= - )[-]\s))"
time = "(?P<time>(?<=\[).*(?=\]))"
request = "(?P<request>POST.*(?=\"))"

h_u = host+user_name

logdata = """168.95.156.240 - stark2413 [21/Jun/2019:15:45:31 -0700] "GET /engage HTTP/2.0" 201 9645
71.172.239.195 - dooley1853 [21/Jun/2019:15:45:32 -0700] "PUT /cutting-edge HTTP/2.0" 406 24498
180.95.121.94 - mohr6893 [21/Jun/2019:15:45:34 -0700] "PATCH /extensible/reinvent HTTP/1.1" 201 27330
144.23.247.108 - auer7552 [21/Jun/2019:15:45:35 -0700] "POST /extensible/infrastructures/one-to-one/enterprise HTTP/1.1" 100 22921
2.179.103.97 - lind8584 [21/Jun/2019:15:45:36 -0700] "POST /grow/front-end/e-commerce/robust HTTP/2.0" 304 14641
241.114.184.133 - tromp8355 [21/Jun/2019:15:45:37 -0700] "GET /redefine/orchestrate HTTP/1.0" 204 29059"""

for item in re.finditer(h_u, logdata):
    print(item.groupdict()) 

单独提取host的结果 #

{'host': '146.204.224.152'}
{'host': '197.109.77.178'}
{'host': '156.127.178.177'}
{'host': '100.32.205.59'}
{'host': '168.95.156.240'}
{'host': '71.172.239.195'}
{'host': '180.95.121.94'}

问题原因 #

两个正则的预查逻辑冲突：

• host使用正向预查(?= - )，仅验证IP后紧跟-但不消耗该字符
• user_name开头带空格，且用反向预查(?<= - )要求前面是-

合并后，host匹配IP后，-未被消耗，此时user_name需要匹配的位置前是IP的最后一位，不满足反向预查的-要求，导致整体匹配失败。

修复方案 #

去掉多余的预查逻辑，直接匹配实际存在的连接字符-，将两个正则整合为完整的匹配结构：

import re

# 简化后的合并正则
h_u = "(?P<host>[\d]{1,3}(?:\.[\d]{1,3}){3}) - (?P<user_name>[a-zA-Z]+\d+|-\s?)"

logdata = """168.95.156.240 - stark2413 [21/Jun/2019:15:45:31 -0700] "GET /engage HTTP/2.0" 201 9645
71.172.239.195 - dooley1853 [21/Jun/2019:15:45:32 -0700] "PUT /cutting-edge HTTP/2.0" 406 24498
180.95.121.94 - mohr6893 [21/Jun/2019:15:45:34 -0700] "PATCH /extensible/reinvent HTTP/1.1" 201 27330
144.23.247.108 - auer7552 [21/Jun/2019:15:45:35 -0700] "POST /extensible/infrastructures/one-to-one/enterprise HTTP/1.1" 100 22921
2.179.103.97 - lind8584 [21/Jun/2019:15:45:36 -0700] "POST /grow/front-end/e-commerce/robust HTTP/2.0" 304 14641
241.114.184.133 - tromp8355 [21/Jun/2019:15:45:37 -0700] "GET /redefine/orchestrate HTTP/1.0" 204 29059"""

for item in re.finditer(h_u, logdata):
    print(item.groupdict()) 

运行后即可得到包含host和user_name的正确匹配结果：

{'host': '168.95.156.240', 'user_name': 'stark2413'}
{'host': '71.172.239.195', 'user_name': 'dooley1853'}
{'host': '180.95.121.94', 'user_name': 'mohr6893'}
{'host': '144.23.247.108', 'user_name': 'auer7552'}
{'host': '2.179.103.97', 'user_name': 'lind8584'}
{'host': '241.114.184.133', 'user_name': 'tromp8355'}

内容的提问来源于stack exchange，提问作者Aaryan Kandiah