Simplifying Python string regex/pattern matching

Question

The following code does what I want:

if myString.startswith(", "):
    myString = myString.lstrip(", ")
if myString.endswith(", "):
    myString = myString.rstrip(", ")
if re.search(", ,", myString):
   myString = re.sub(", ,", "", myString)

Basically, I want it to remove any leading commas, trailing commas, and anywhere two commas appear without anything in between them. This does the trick, but I am betting there is a way to simplify this to make it more elegant and use fewer lines of code.

Any suggestions would really be appreciated. Thanks in advance!

Fewer lines of code != simplification. Why not just always run lstrip, rstrip and re.sub, if it can't find any matches it will return the un-altered string — Daan Timmer
– Daan Timmer, Commented Aug 27, 2013 at 7:33

Sukrit Kalra · Accepted Answer · 2013-08-27 07:57:29Z

8

For a starter, I'd use .strip, which has both rstrip and lstrip. And then, replace for the two commas:

MyString = MyString.strip(", ").replace(", , ", "")

edited Aug 27, 2013 at 7:57

Sukrit Kalra

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answered Aug 27, 2013 at 7:37

Jblasco

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Comments

falsetru · Accepted Answer · 2013-08-27 07:37:10Z

2

Using split + join:

>>> s = ', a, b, ,c, '
>>> ', '.join(x for x in map(str.strip, s.split(',')) if x)
'a, b, c'

answered Aug 27, 2013 at 7:37

falsetru

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Comments

Jan Zeiseweis · Accepted Answer · 2013-08-27 07:38:02Z

1

You could use re.sub:

import re
myString = re.sub('^, |, $|, ,', '', myString)

answered Aug 27, 2013 at 7:38

Jan Zeiseweis

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Comments

eminor · Accepted Answer · 2013-08-27 08:49:58Z

1

The code from the answers compared with timeit:

s = ", 1, 2, , 3, 4, , 5, 6, , 7, 8, , 9, 10, , 11, 12, , 13, 14, , 15, 16 ,"

def f1(s):
    s = s.strip(", ").replace(", , ", "")

def f2(s):
    s = ', '.join(x for x in map(str.strip, s.split(',')) if x)

def f3(s):
    s = re.sub('^, |, $|, ,', '', s)

if __name__ == '__main__':
    import timeit, re

    print(timeit.timeit("f1(s)", setup="from __main__ import f1, s"))
    print(timeit.timeit("f2(s)", setup="from __main__ import f2, s"))
    print(timeit.timeit("f3(s)", setup="from __main__ import f3, s"))

Results (on my netbook):

1.44931602478
13.0764448643
11.3456158638

edited Aug 27, 2013 at 8:49

answered Aug 27, 2013 at 8:42

eminor

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Comments

Himanshu · Accepted Answer · 2013-08-27 07:38:40Z

0

You probably want that , , replaced by , instead of nothing.

>>> " ,a,b,,c, ".strip(' ,').replace(',,', ',')
'a,b,c'

answered Aug 27, 2013 at 7:38

Himanshu

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