Escaping regex string in Python
I want to use input from a user as a regex pattern for a search over some text. It works, but how I can handle cases where user puts characters that have meaning in regex? For example, the user wants to search for Word (s)
: regex engine will take the (s)
as a group. I want it to treat it like a string "(s)"
. I can run replace
on user input and replace the (
with (
and the )
with )
but the problem is I will need to do replace for every possible regex symbol. Do you know some better way ?
Use the re.escape()
function for this:
4.2.3 re
Module Contents
escape(string)
Return string with all non-alphanumerics backslashed; this is useful if you want to match an arbitrary literal string that may have regular expression metacharacters in it.
A simplistic example, search any occurence of the provided string optionally followed by 's', and return the match object.
def simplistic_plural(word, text):
word_or_plural = re.escape(word) + 's?'
return re.match(word_or_plural, text)
You can use re.escape():
re.escape(string) Return string with all non-alphanumerics backslashed; this is useful if you want to match an arbitrary literal string that may have regular expression metacharacters in it.
>>> import re
>>> re.escape('^a.*$')
'^a.*$'
Unfortunately, re.escape()
is not suited for the replacement string:
>>> re.sub('a', re.escape('_'), 'aa')
'__'
A solution is to put the replacement in a lambda:
>>> re.sub('a', lambda _: '_', 'aa')
'__'
because the return value of the lambda is treated by re.sub()
as a literal string.
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