Question

我在其他帖子中看到，这是在执行(?<!X|Y|Z)时解决非固定宽度模式问题的正确方法，但对我不起作用。

我正在尝试以下

re.search(r'\b(?:(?<!Yummy)|(?<!Xoo))\bfoo\b', "Yummy foo", flags=re.UNICODE) is not None => True
re.search(r'\b(?:(?<!Yummy)|(?<!Xoo))\bfoo\b', "Xoo foo", flags=re.UNICODE) is not None => True
re.search(r'\b(?:(?<!Yummy)|(?<!Xoo))\bfoo\b', "other Yummy  foo someone", flags=re.UNICODE) is not None => True

当它返回False时，它总是返回True。现在，如果我删除或|，它可以正常工作。

re.search(r'\b(?:(?<!Yummy))\bfoo\b', "Yummy foo", flags=re.UNICODE) is not None => False
re.search(r'\b(?<!Yummy)\bfoo\b', "Yummy foo", flags=re.UNICODE) is not None => False
re.search(r'\b(?<!Yummy)\bfoo\b', " Yummy  foo", flags=re.UNICODE) is not None => False
re.search(r'\b(?<!Yummy)\bfoo\b', "other Yummy foo someone", flags=re.UNICODE) is not None => False
re.search(r'\b(?<!Yummy)\bfoo\b', "foo someone", flags=re.UNICODE) is not None => True
re.search(r'\b(?<!Yummy)\bfoo\b', "foo", flags=re.UNICODE) is not None => True

有什么建议吗？

Answer 1

你不需要使用替换，因为lookbehinds是零宽度断言，你可以这样写：

re.search(r'\b(?<!\bYum)(?<!\bXooop)\s+foo\b', "Yum foo", flags=re.UNICODE)
            ^ ^         ^
            | |         |
            +-+---------+---These three assertions are tested at the same
                            position (i.e. immediatly before the \s+ match.
                            You can put them in any order you want, they are
                            only checks and don't eat characters.

正则表达式后视问题

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