带有惰性量词的环顾四周

Question

我正在尝试在正则表达式中使用 lookbehind，然后使用惰性“匹配所有模式”(.+?)，但我想知道我是否可以通过这种方式使用 lookarounds。

例如，我有以下正则表达式：(?<!learn).+?write a regex

"I'm learning how to write a regex" (应该不匹配)
"I know how to write a regex" （应该匹配）
"I know how to read an write a regex" （应该匹配）
"I want to know how to write a regex" （应该匹配）
"I want to learn how to write a regex" (应该不匹配)

如果你使用上面的正则表达式，你会得到匹配的所有内容。

Answer 1

您的模式匹配所有行，因为 (?<!learn).+?write a regex 将运行在第一个位置向后看，断言当前位置左侧的内容不是 learn

断言为真，这部分将立即匹配，直到第一次出现 write a regex

你可以做的是利用 PyPi regex module 支持后视的无限量词：

(?<!\blearn.+?)\bwrite a regex\b

Regex demo | Python demo

import regex

pattern = r"(?<!\blearn.+?)\bwrite a regex\b"

strings = [
    "I'm learning how to write a regex",
    "I know how to write a regex",
    "I know how to read an write a regex",
    "I want to know how to write a regex",
    "I want to learn how to write a regex"
]

for s in strings:
    if regex.search(pattern, s):
        print(s)

输出

I know how to write a regex
I know how to read an write a regex
I want to know how to write a regex

带有惰性量词的环顾四周

Lookarounds with lazy quantifiers

regex

python-3.x

regex-lookarounds