Python regex, remove all punctuation except hyphen for unicode string

Question

I have this code for removing all punctuation from a regex string:

import regex as re    
re.sub(ur"\p{P}+", "", txt)

How would I change it to allow hyphens? If you could explain how you did it, that would be great. I understand that here, correct me if I'm wrong, P with anything after it is punctuation.

Answer 1

[^\P{P}-]+

\P is the complementary of \p - not punctuation. So this matches anything that is not (not punctuation or a dash) - resulting in all punctuation except dashes.

Example: http://www.rubular.com/r/JsdNM3nFJ3

If you want a non-convoluted way, an alternative is \p{P}(?<!-): match all punctuation, and then check it wasn't a dash (using negative lookbehind).
Working example: http://www.rubular.com/r/5G62iSYTdk

Answer 2

Here's how to do it with the re module, in case you have to stick with the standard libraries:

# works in python 2 and 3
import re
import string

remove = string.punctuation
remove = remove.replace("-", "") # don't remove hyphens
pattern = r"[{}]".format(remove) # create the pattern

txt = ")*^%{}[]thi's - is - @@#!a !%%!!%- test."
re.sub(pattern, "", txt) 
# >>> 'this - is - a - test'

If performance matters, you may want to use str.translate, since it's faster than using a regex. In Python 3, the code is txt.translate({ord(char): None for char in remove}).

Answer 3

You could either specify the punctuation you want to remove manually, as in [._,] or supply a function instead of the replacement string:

re.sub(r"\p{P}", lambda m: "-" if m.group(0) == "-" else "", text)