Question

If I have a string

"this is   a    string"

How can I shorten it so that I only have one space between the words rather than multiple? (The number of white spaces is random)

"this is a string"

Answer 1

You could use string.split and " ".join(list) to make this happen in a reasonably pythonic way – there are probably more efficient algorithms but they won’t look as nice.

Incidentally, this is a lot faster than using a regex, at least on the sample string:

import re
import timeit

s = "this    is   a     string"

def do_regex():
    for x in xrange(100000):
        a = re.sub(r'\s+', ' ', s)

def do_join():
    for x in xrange(100000):
        a = " ".join(s.split())


if __name__ == '__main__':
    t1 = timeit.Timer(do_regex).timeit(number=5)
    print "Regex: ", t1
    t2 = timeit.Timer(do_join).timeit(number=5)
    print "Join: ", t2


$ python revsjoin.py 
Regex:  2.70868492126
Join:  0.333452224731

Compiling this regex does improve performance, but only if you do call sub on the compiled regex, instead of passing the compiled form into re.sub as an argument:

def do_regex_compile():
  pattern = re.compile(r'\s+')
  for x in xrange(100000):
    # Don't do this
    # a = re.sub(pattern, ' ', s)
    a = pattern.sub(' ', s)

$ python revsjoin.py  
Regex:  2.72924399376
Compiled Regex:  1.5852200985
Join:  0.33763718605