Replace non alphanumeric characters except some exceptions python

Question

In perl s/[^\w:]//g would replace all non alphanumeric characters EXCEPT :

In python I'm using re.sub(r'\W+', '',mystring) which does remove all non alphanumeric except _ underscore. Is there any way to put exceptions, I wish not to replace signs like = and .

Previously I was applying the other approach i.e. to replace all unwanted characters usingre.sub('[!@#\'\"$()]', '',mystring`) However, it is not possible for me to predict what all characters may come in mystring hence I wish to remove all non alphanumeric characters except a few.

Google didnt provide an appropriate answer. The closest search being python regex split any \W+ with some exceptions but this didnt help me either.

nu11p01n73R · Accepted Answer · 2015-01-14 09:13:15Z

16

You can specify everything that you need not remove in the negated character clas.

re.sub(r'[^\w'+removelist+']', '',mystring)

Test

>>> import re
>>> removelist = "=."
>>> mystring = "asdf1234=.!@#$"
>>> re.sub(r'[^\w'+removelist+']', '',mystring)
'asdf1234=.'

Here the removelist variable is a string which contains the list of all characters you need to exclude from the removal.

What does negated character class means

When the ^ is moved into the character class it does not acts as an anchor where as it negates the character class.

That is ^ in inside a character class say like [^abc] it negates the meaning of the character class.

For example [abc] will match a b or c where as [^abc] will not match a b or c. Which can also be phrased as anything other than a b or c

edited Jan 14, 2015 at 9:13

answered Jan 14, 2015 at 8:51

nu11p01n73R

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4 Comments

pythonRcpp Over a year ago

thanks @nu11p01n73R . I was not adding remove list inside, [] . I gave something like '^w.=' which off course was not working. Could you please tell the meaning of r and ^, ^ is usually used as "start with" but here it seems to be having a different meaning.

nu11p01n73R Over a year ago

@user1977867 Yep when ^ in inside a character class say like [^abc] it negates the meaning of the character class. That is [abc] will match a b or c where as [^abc] will not match a b or c. That is anything other than a b or c

ikku100 Over a year ago

Can I ask why you're calling removelist 'remove'list? It seems to me that it's a list of chars that you'd like to keep. I'm only mentioning it because it had me confused.

nu11p01n73R Over a year ago

@ikku100 Ohh, I have mentioned it in the answer Here the removelist variable is a string which contains the list of all characters you need to exclude from the removal.

vks · Accepted Answer · 2015-01-14 08:50:15Z

10

re.sub(r'[^a-zA-Z0-9=]', '',mystring)

You can add whatever you want like _ whichever you want to save.

answered Jan 14, 2015 at 8:50

vks

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Comments

maillard · Accepted Answer · 2015-01-14 08:49:16Z

7

I believe the approach you describe in perl could also be used in python, eg:

re.sub(r'[^\w=]', '',mystring)

would remove everything except word-characters and =

answered Jan 14, 2015 at 8:49

maillard

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