如果前面没有否定词，则正则表达式包含词[重复]答案

【问题标题】：Regex contains words if no negative words are before it [duplicate]如果前面没有否定词，则正则表达式包含词[重复]
【发布时间】：2020-12-27 00:52:12
【问题描述】：

我想抓取说 good 或 great 但未被 not 或 isn't 否定的短语 之前。

sents= ["good words",                   # Words after phrase
        "not good words",
        "isn't good words",

        "great words",
        "not great words",
        "isn't great words",



        "words good",                   # Words before phrase
        "words not good",
        "words isn't good"

        "words great",
        "words not great",
        "words isn't great"


        
        "words good words",             # Words before and after phrase
        "words not good words",
        "words isn't good words",

        "words great words",
        "words not great words",
        "words isn't great words",
]

我想回来

good words
words good
words good words

great words
words great
words great words

让我这样做的正则表达式是什么？从理论上讲，我希望能够有一个单词列表，只有当字符串不包含任何来自否定列表的单词时才能找到它。

【问题讨论】：

标签： python regex

【解决方案1】：

您可以在 python 中将此正则表达式与 2 个否定的后向断言一起使用：

(?<!isn't )(?<!not )\b(?:good|great)\b

RegEx Demo

正则表达式详细信息：

(?<!isn't )：如果我们有 isn't 后面跟一个空格，则负向后看会导致匹配失败
(?<!not )：如果我们有 not 后面跟一个空格，则负向后看会导致匹配失败
\b：字边界
(?:good|great)：匹配 good 或 great
\b：字边界

代码：

>>> sents= ["good words",                   # Words after phrase
...         "not good words",
...         "isn't good words",
...         "great words",
...         "not great words",
...         "isn't great words",
...         "words good",                   # Words before phrase
...         "words not good",
...         "words isn't good",
...         "words great",
...         "words not great",
...         "words isn't great",
...         "words good words",             # Words before and after phrase
...         "words not good words",
...         "words isn't good words",
...         "words great words",
...         "words not great words",
...         "words isn't great words",
... ]
>>> reg = re.compile(r"(?<!isn't )(?<!not )\b(?:good|great)\b")
>>> for s in sents:
...     if reg.search(s):
...             print(s)
...
good words
great words
words good
words great
words good words
words great words

【讨论】：

【解决方案2】：

您需要使用 look behind，在本例中为 negative，因为也有 positive 的版本。你可以像这样简单地使用它：

(?<!not\s)great

在此示例中，单词 not 不能存在于 great 之前。

下面是它的样子：

(?<!not\s)(?<!isn't\s)(great|good)

Online Demo

【讨论】：