How to rermove non-alphanumeric characters at the beginning or end of a string

Question

I have a list with elements that have unnecessary (non-alphanumeric) characters at the beginning or end of each string.

Ex.

\'cats--\'

Answer 1

By using strip you have to know the substring to be stripped.

>>> 'cats--'.strip('-')
'cats'

You could use re to get rid of the non-alphanumeric characters but you would shoot with a cannon on a mouse IMO. With str.isalpha() you can test any strings to contain alphabetic characters, so you only need to keep those:

>>> ''.join(char for char in '#!cats-%' if char.isalpha())
'cats'
>>> thelist = ['cats5--', '#!cats-%', '--the#!cats-%', '--5cats-%', '--5!cats-%']
>>> [''.join(c for c in e if c.isalpha()) for e in thelist]
['cats', 'cats', 'thecats', 'cats', 'cats']

You want to get rid of non-alphanumeric so we can make this better:

>>> [''.join(c for c in e if c.isalnum()) for e in thelist]
['cats5', 'cats', 'thecats', '5cats', '5cats']

This one is exactly the same result you would get with re (as of Christian's answer):

>>> import re
>>> [re.sub("[^\\w]", "", e) for e in thelist]
['cats5', 'cats', 'thecats', '5cats', '5cats']

However, If you want to strip non-alphanumeric characters from the end of the strings only you should use another pattern like this one (check re Documentation):

>>> [''.join(re.search('^\W*(.+)(?!\W*$)(.)', e).groups()) for e in thelist]
['cats5', 'cats', 'the#!cats', '5cats', '5!cats']