Issue with regex backreference in Python

Question

I am not sure why this is not working. Perhaps I am missing something with Python regex.

Here is my regex and an example string of what I want it to match too:

    PHONE_REGEX        = "<(.*)>phone</\1>"
    EXAMPLE            = "<bar>phone</bar>"

I tested this match in isolation and it failed. I used an online regex tester and it matched. Am I simply missing something that is particular to Python regex?

Thanks!

Simeon Visser · Accepted Answer · 2012-03-24 16:09:37Z

8

You have to mark the string as a raw string, due to the \ in there, by putting an r in front of the regex:

m = re.match(r"<(.*)>phone</\1>", "<bar>phone</bar>")

answered Mar 24, 2012 at 16:09

Simeon Visser

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2 Comments

PFranchise Over a year ago

Ok, thanks! Is that required anytime a '\' is used? Or just in instances it is used for back-referencing?

Simeon Visser Over a year ago

If the first parameter is a variable, just make sure all backslashes are escaped with another backslash in front of it. The following will work as well: "<(.*)>phone</\\1>". It's just that \ has a special meaning in a regex and you'll need to escape it if you literally wish to use a \.

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