Extracting alphanumeric substring from a string in python

Question

i have a string in python

text = '(b)'

i want to extract the 'b'. I could strip the first and the last letter of the string but the reason i wont do that is because the text string may contain '(a)', (iii), 'i)', '(1' or '(2)'. Some times they contain no parenthesis at all. but they will always contain an alphanumeric values. But i equally want to retrieve the alphanumeric values there.

this feat will have to be accomplished in a one line code or block of code that returns justthe value as it will be used in an iteratively on a multiple situations

what is the best way to do that in python,

score 4 · Accepted Answer · 2014-06-12 00:58:45Z

4

I don't think Regex is needed here. You can just strip off any parenthesis with str.strip:

>>> text = '(b)'
>>> text.strip('()')
'b'
>>> text = '(iii)'
>>> text.strip('()')
'iii'
>>> text = 'i)'
>>> text.strip('()')
'i'
>>> text = '(1'
>>> text.strip('()')
'1'
>>> text = '(2)'
>>> text.strip('()')
'2'
>>> text = 'a'
>>> text.strip('()')
'a'
>>>

Regarding @MikeMcKerns' comment, a more robust solution would be to pass string.punctuation to str.strip:

>>> from string import punctuation
>>> punctuation  # Just to demonstrate
'!"#$%&\'()*+,-./:;<=>?@[\\]^_`{|}~'
>>>
>>> text = '*(ab2**)'
>>> text.strip(punctuation)
'ab2'
>>>

edited Jun 12, 2014 at 0:58

answered Jun 12, 2014 at 0:39

user2555451

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3 Comments

Mike McKerns Over a year ago

doesn't handle *(ab2**)

user2555451 Over a year ago

@MikeMcKerns - Well, in that case, you could always do text.strip(string.punctuation).

Mike McKerns Over a year ago

Then that should be your answer.

Avinash Raj · Accepted Answer · 2014-06-12 00:57:44Z

2

You could do this through python's re module,

>>> import re
>>> text = '(5a)'
>>> match = re.search(r'\(?([0-9A-Za-z]+)\)?', text)
>>> match.group(1)
'5a'
>>> text = '*(ab2**)'
>>> match = re.search(r'\(?([0-9A-Za-z]+)\)?', text)
>>> match.group(1)
'ab2'

answered Jun 12, 2014 at 0:57

Avinash Raj

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Comments

Mike McKerns · Accepted Answer · 2014-06-12 00:49:26Z

2

Not fancy, but this is pretty generic

>>> import string
>>> ''.join(i for i in text if i in string.ascii_letters+'0123456789')

This works for all sorts of combinations of parenthesis in the middle of the string, and also if you have other non-alphanumeric characters (aside from the parenthesis) present.

edited Jun 12, 2014 at 0:49

answered Jun 12, 2014 at 0:43

Mike McKerns

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Comments

agamike · Accepted Answer · 2014-06-12 00:52:41Z

0

re.match(r'\(?([a-zA-Z0-9]+)', text).group(1)

for your input provided by exmple it would be:

>>> a=['(a)', '(iii)', 'i)', '(1' , '(2)']
>>> [ re.match(r'\(?([a-zA-Z0-9]+)', text).group(1) for text in a ]
['a', 'iii', 'i', '1', '2']

edited Jun 12, 2014 at 0:52

answered Jun 12, 2014 at 0:46

agamike

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