Python re 模块中的正则表达式是否支持单词边界 (\b)？
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Do regular expressions from the re module support word boundaries (\b)?
提问by D.C.
While trying to learn a little more about regular expressions, a tutorial suggested that you can use the \bto match a word boundary. However, the following snippet in the Python interpreter does not work as expected:
在尝试了解更多有关正则表达式的知识时，一个教程建议您可以使用\b来匹配单词边界。但是，Python 解释器中的以下代码段无法按预期工作：
>>> x = 'one two three'
>>> y = re.search("\btwo\b", x)
It should have been a match object if anything was matched, but it is None.
如果有任何匹配，它应该是一个匹配对象，但它是None.
Is the \bexpression not supported in Python or am I using it wrong?
\bPython 不支持该表达式还是我使用错误？
采纳答案by pyfunc
Why don't you try
你为什么不试试
word = 'two'
re.compile(r'\b%s\b' % word, re.I)
Output:
输出：
>>> word = 'two'
>>> k = re.compile(r'\b%s\b' % word, re.I)
>>> x = 'one two three'
>>> y = k.search( x)
>>> y
<_sre.SRE_Match object at 0x100418850>
Also forgot to mention, you should be using raw stringsin your code
>>> x = 'one two three'
>>> y = re.search(r"\btwo\b", x)
>>> y
<_sre.SRE_Match object at 0x100418a58>
>>>
回答by Bolo
This will work: re.search(r"\btwo\b", x)
这将起作用： re.search(r"\btwo\b", x)
When you write "\b"in Python, it is a single character: "\x08". Either escape the backslash like this:
当您用"\b"Python编写时，它是单个字符："\x08". 要么像这样逃避反斜杠：
"\b"
or write a raw string like this:
或者写一个像这样的原始字符串：
r"\b"
回答by Bill the Lizard
Just to explicitly explain whyre.search("\btwo\b", x)doesn't work, it's because \bin a Python string is shorthand for a backspace character.
只是为了明确解释为什么re.search("\btwo\b", x)不起作用，这是因为\b在 Python 中字符串是退格字符的简写。
print("foo\bbar")
fobar
So the pattern "\btwo\b"is looking for a backspace, followed by two, followed by another backspace, which the string you're searching in (x = 'one two three') doesn't have.
所以该模式"\btwo\b"正在寻找一个退格，然后是two，然后是另一个退格，您在 ( x = 'one two three') 中搜索的字符串没有。
To allow re.search(or compile) to interpret the sequence \bas a word boundary, either escape the backslashes ("\\btwo\\b") or use a raw string to create your pattern (r"\btwo\b").
要允许re.search（或compile）将序列解释\b为单词边界，请转义反斜杠 ( "\\btwo\\b") 或使用原始字符串来创建模式 ( r"\btwo\b")。
