How to remove nonalphanumeric character in python but keep some special characters

Question

I figure out how to remove special non alphanumeric character in python using the following function:

p_nonalphanum = re.compile('\W+') def removeNonAlphaNum(string): m = p_nonalphanum.match(string) if m: string = string[m.end():] return string

I would like to keep some specials characters though such as ½, ¾ which i consider as number. How should i edit my regex?

e.g: from "• ½ cup flour" to "½ cup flour"

Are you sure this is working for you so far? >>> removeNonAlphaNum('-hello-') 'hello-' — jamylak
– jamylak, Commented May 25, 2012 at 9:33
Only non alpha num characters starting in a string matters to me but this could be extended — tiguero
– tiguero, Commented May 25, 2012 at 10:21

stema · Accepted Answer · 2012-05-25 10:07:03Z

3

You can use a negated character class and add all characters you want to keep

You could do something like this:

p_nonalphanum = re.compile('[^\w½¾]+') print (p_nonalphanum.sub('', test))

edited May 25, 2012 at 10:07

answered May 25, 2012 at 9:34

stema

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2 Comments

tiguero Over a year ago

this sounds like the first good solution as i want to edit my regex but I have this error message: SyntaxError: Non-ASCII character '\xc2' in file

tiguero Over a year ago

ok i just need to add this first line in my python script: # -- coding: utf-8 --

johnsyweb · Accepted Answer · 2012-05-25 09:57:59Z

>>> def remove_unwanted(s): ... '''• ½ cup flour -> ½ cup flour''' ... allowed = '[\w½¾]+' ... return ' '.join(re.findall(allowed, s)) ... >>> print remove_unwanted('• ½ cup flour ->') ½ cup flour

Nolen Royalty · Accepted Answer · 2012-05-25 10:13:36Z

Don't bother with a regex where you manually add each character you want, use the builtin isalnum function!

>>> s = "• ½ cup flour -> ½ cup flour" >>> def only_alphanum(s): ... s = unicode(s, "utf-8") ... return ' '.join(c for c in s.split() if c.isalnum()) ... >>> print only_alphanum(s) ½ cup flour ½ cup flour

This will let you catch any fraction, instead of just the list of fractions that you've assembled in your regex(which could get long very quickly)

>>> s = "• ¼ cup oats -*(*&!!" >>> print only_alphanum(s) ¼ cup oats

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