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Pretty print an integer

Exercise: Take an integer and print it in a pretty way, i.e. use commas as thousands separators. Example: 1977 should be 1,977.

Solution:

#!/usr/bin/env python

def numberToPrettyString(n):
    """Converts a number to a nicely formatted string.
       Example: 6874 => '6,874'."""
    l = []
    for i, c in enumerate(str(n)[::-1]):
        if i%3==0 and i!=0:
            l += ','
        l += c
    return "".join(l[::-1])
#

if __name__ == "__main__":
    number = 6874
    print numberToPrettyString(number)   # '6,874'

The idea is simple. Consider the number 1977. Convert it to string ("1977") and reverse it ("7791"). Start processing it from left to right and after every third character add a comma: "7" -> "77" -> "779," (comma added) -> "779,1". Now reverse the string ("1,977"). Done.

Links

Update (20131125)
There is an easier way. You can do it with string formatting too:

>>> n = 1977
>>> "{:,}".format(n)
'1,977'

Thanks to Krisztián B. for the tip.

Categories: python Tags: , , ,
  1. July 1, 2014 at 21:35

    This should work on older Python versions:

    >>> import locale
    >>> locale.setlocale(locale.LC_ALL, 'en_US')
    'en_US'
    >>> locale.format("%d", 1255000, grouping=True)
    '1,255,000'
    

    http://stackoverflow.com/questions/1823058/how-to-print-number-with-commas-as-thousands-separators-in-python-2-x

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