Python正则表达式未返回预期结果：如何调整正则规则？

原代码问题原因 #

• 正则中的.未转义：.在正则里是匹配任意字符的通配符，原代码前瞻里的. Withey Limited实际是匹配任意字符加空格Withey Limited，完全偏离了匹配字面句号的需求。
• 贪婪匹配+错误的字符集：原正则用了贪婪的+匹配，且字符集包含.，导致会把It was formerly known as 后面的内容一直匹配到最远的前瞻位置（也就是. It），连本该保留的. Withey Limited也被包含进匹配范围，替换后只剩后面的. It...。
• 前瞻未做优先匹配：原代码把两个停止条件放在同一个前瞻里，贪婪模式下会选择最远的匹配项，无法实现优先在. Withey Limited停止的需求。

修正后的代码 #

使用非贪婪匹配+分支优先的正则，就能得到预期结果：

import re
txt = 'It was formerly known as A. Withey & Black Limited. Withey Limited delivers many things. It has a facility in the UK, including many branches.'
# 方案1：用前瞻定位停止点，替换掉前面的内容
out = re.sub(r'\s*It was formerly known as .*?(?=\. Withey Limited|\. It)', '', txt)
# 方案2：捕获停止点内容，替换为捕获组（效果一致）
# out = re.sub(r'\s*It was formerly known as .*?(\. Withey Limited|\. It)', r'\1', txt)
print(out)

修正说明 #

• 非贪婪匹配.*?：确保匹配到第一个符合条件的停止点就停止，不会过度匹配。
• 转义句号\.：明确匹配字面的句号，避免通配符干扰。
• 分支顺序优先：把\. Withey Limited放在分支前面，正则会优先匹配这个停止点，只有当不存在时才匹配\. It，符合需求。

运行后输出：

Withey Limited delivers many things. It has a facility in the UK, including many branches.

内容的提问来源于stack exchange，提问作者Eghbal