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What the title says. No more, no less. (Version 2, now supports negative numbers.)

Python, 12 lines
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def group(n, sep = ','):
    s = str(abs(n))[::-1]
    groups = []
    i = 0
    while i < len(s):
        groups.append(s[i:i+3])
        i+=3
    retval = sep.join(groups)[::-1]
    if n < 0:
        return '-%s' % retval
    else:
        return retval

I'm sure there's a similar or better implementation somewhere in the cookbook, I was just too lazy to search properly; besides, it is so simple that I'm not sure if it even deserves an entry.

Examples:

>>> group(42)
'42'
>>> group(4242)
'4,242'
>>> group(42424242)
'42,424,242'
>>> group(42424242, "'")
"42'424'242"
>>> group(-424)
'-424'

3 comments

Steven Bethard 16 years, 3 months ago  # | flag

Note that the locale module does most of what you want here:

py> import locale
py> locale.setlocale(locale.LC_ALL, '')
'English_United States.1252'
py> locale.format('%i', 42, True)
'42'
py> locale.format('%i', 4242, True)
'4,242'
py> locale.format('%i', 424242, True)
'424,242'
py> locale.format('%i', 42424242, True)
'42,424,242'
Walter Brunswick 16 years, 3 months ago  # | flag

Error... Nevertheless Mr. Bethard, it is an interesting definition. However, I found that it faults when supplied a decimal or a float.

>>> group(44.44)
'44,.44'
Phil Huffman 10 years, 5 months ago  # | flag

Here's my solution to the problem. It's designed to work for any real number.

def group_digits(number = 0, separator = ',', group_size = 3):
    if (number < 0):
        prefix = '-'
        number = -number;
    else:
        prefix = ''
    string = "{0}".format(number)
    dot_index = string.find('.');
    string_size = len(string) if dot_index == -1 else dot_index

    if string_size > group_size:
        groups = []
        first_group_size = string_size % group_size;
        if first_group_size:
            groups.append(string[0:first_group_size])
        for i in range(first_group_size, string_size, group_size):
            groups.append(string[i:i+group_size])
        return_string = separator.join(groups)
       return_string = return_string if dot_index == -1 else return_string + string[dot_index:]
    else:
        return_string = string

    return prefix + return_string
Created by Marek Baczynski on Wed, 17 Aug 2005 (PSF)
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