1   Using str.format

With str.format, format specifier for thousands separator is support by PEP 378, for example:

>>> '{:15,f}'.format(54321.123)
'  54,321.123000'

>>> '{:15,f}'.format(54321.123).replace(",", "X").replace(".", ",").replace("X", ".")
'  54.321,123000'

>>> '{:15,f}'.format(54321.123).replace(",", " ")
'  54 321.123000'

2   Using locale

If str.format isnt available as the Python is older than 2.6, then you can use locale, for example:

import locale
locale.setlocale(locale.LC_ALL, 'en_US')
print locale.format("%d", 7654321, grouping=True)
print locale.format("%f", 7654321.12345, grouping=True)

But this method relies on what locale is available on the system, its more likely to be an issue when running a script in different system since not all systems are built the same.

3   Using intcomma

Or write own code:

def intcomma(n):
  sign = '-' if n < 0 else ''
  n = str(abs(n)).split('.')
  dec = '' if len(n) == 1 else '.' + n[1]
  # A)
  # n = ' '*(3-len(n[0])%3) + n[0]
  # return sign + (','.join([n[i*3:(i+1)*3] for i in range(len(n)/3)])).lstrip(' ,') + dec
  # B)
  n = n[0]
  m = len(n)
  # B-1)
  # return sign + ','.join(filter(None, [n[0:m%3]] + [n[i:i+3] for i in range(m%3, m, 3)])) + dec
  # B-2)
  return sign + (','.join([n[0:m%3]] + [n[i:i+3] for i in range(m%3, m, 3)])).lstrip(',') + dec

Its named after intcomma filter from Djangos humanize. The method A prepends spaces so the string format of the number will be len(n)%3 == 0. The method B-1 and B-2 use different way to extract part of number (the part before first thousands separator), then take 3 digits after each time. By the way, in method A, I finally have one reasonable usage of str.lstrip([chars]). Note that there is a reason why Python doc uses [chars] not str_to_strip.

A quick test:

print intcomma(0)
print intcomma(1)
print intcomma(21)
print intcomma(321)
print intcomma(4321)
print intcomma(54321)
print intcomma(654321)
print intcomma(7654321)
print
print intcomma(4321.1234)
print
print intcomma(-0)
print intcomma(-1)
print intcomma(-21)
print intcomma(-321)
print intcomma(-4321)
print intcomma(-54321)
print intcomma(-654321)
print intcomma(-7654321)
print
print intcomma(-4321.1234)
print

0
1
21
321
4,321
54,321
654,321
7,654,321

4,321.1234

0
-1
-21
-321
-4,321
-54,321
-654,321
-7,654,321

-4,321.1234

4   Changes

• 2013-07-28T06:30:30Z: add builtin format specifier.