intsep.py

from itertools import izip_longest

def intseparator(value, separator=" ", group_every=3):
    if '.' in value or ',' in value:
        return value

    def grouper(n, iterable, padvalue=None):
        return izip_longest(*[iter(iterable)] * n, fillvalue=padvalue)

    return separator.join(map(''.join, grouper(group_every, reversed(value), '')))[::-1]


import re

def intseparator_old(value, separator=" "):
    new = re.sub("^(-?\d+)(\d{3})", '\g<1>' + separator + '\g<2>', value)
    if value == new:
        return new
    else:
        return intseparator_old(new, separator)


from timeit import Timer
from random import randint
from functools import partial

vals = ['123', '123.32', '160,23'] + [str(randint(1, 9) * (10 ** randint(1, 9))) for one in range(20)]

for i, one in enumerate(vals):
    print '===', one
    print 'new', Timer(partial(intseparator, one)).timeit(number=10000)
    print 'old', Timer(partial(intseparator_old, one)).timeit(number=10000)

'''
=== 123
new 0.0551390647888
old 0.0619730949402
=== 123.32
new 0.00204801559448
old 0.0639929771423
=== 160,23
new 0.00232195854187
old 0.0642800331116
=== 400000000
new 0.040027141571
old 0.250786781311
=== 2000000
new 0.0401909351349
old 0.24866104126
=== 2000
new 0.0389459133148
old 0.151959896088
=== 40000
new 0.0383281707764
old 0.15451002121
=== 6000000
new 0.0401420593262
old 0.247751951218
=== 5000
new 0.0387279987335
old 0.153437852859
=== 200
new 0.0362091064453
old 0.0630459785461
=== 20000
new 0.0388009548187
old 0.154855966568
=== 400
new 0.0361289978027
old 0.0620431900024
=== 700000000
new 0.0403130054474
old 0.253783941269
=== 800000
new 0.0393478870392
old 0.154774904251
=== 90000
new 0.0382339954376
old 0.154028177261
=== 400
new 0.0360498428345
old 0.059700012207
=== 800000
new 0.0389120578766
old 0.154366970062
=== 200
new 0.0356450080872
old 0.0606961250305
=== 10000
new 0.0382850170135
old 0.15410399437
=== 600000
new 0.0388000011444
old 0.155707836151
=== 100000000
new 0.0406899452209
old 0.250066995621
=== 50000
new 0.0386528968811
old 0.154365062714
=== 300
new 0.0361127853394
old 0.0604050159454
'''