Gareth Rees <[email protected]> added the comment:
The way to avoid this behaviour is to disallow the attempts at matching that
you know are going to fail. As Serhiy described above, if the search fails
starting at the first character of the string, it will move forward and try
again starting at the second character. But you know that this new attempt must
fail, so you can force the regular expression engine to discard the attempt
immediately.
Here's an illustration in a simpler setting, where we are looking for all
strings of 'a' followed by 'b':
>>> import re
>>> from timeit import timeit
>>> text = 'a' * 100000
>>> timeit(lambda:re.findall(r'a+b', text), number=1)
6.643531181000014
We know that any successful match must be preceded by a character other than
'a' (or the beginning of the string), so we can reject many unsuccessful
matches like this:
>>> timeit(lambda:re.findall(r'(?:^|[^a])(a+b)', text), number=1)
0.003743481000014981
In your case, a successful match must be preceded by [^a-zA-Z0-9_.+-] (or the
beginning of the string).
----------
nosy: [email protected]
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<https://bugs.python.org/issue46065>
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