Python human file size

human_size.py

#!/usr/bin/env/python3
import math

def round_down(n, d=8):
    # https://stackoverflow.com/a/43533589/119527
    d = 10 ** d
    return math.floor(n * d) / d

def human_size(n, decimal_places=2):
    n = float(n)

    suffixes = ['', 'Ki', 'Mi', 'Gi', 'Ti', 'Pi']
    for suffix in suffixes:
        if n < 1024:
            break
        n /= 1024

    if n.is_integer():
        size = str(int(n))
    else:
        size = '{0:.{1}f}'.format(round_down(n, decimal_places), decimal_places)

    return '{} {}B'.format(size, suffix)

    
if __name__ == '__main__':
    import unittest

    class Test(unittest.TestCase):
        def test_1(self):
            self.assertEqual(human_size(1), '1 B')

        def test_1000(self):
            self.assertEqual(human_size(1000), '1000 B')

        def test_1_K_minus_1(self):
            self.assertEqual(human_size(1023), '1023 B')

        def test_1_K(self):
            self.assertEqual(human_size(1024), '1 KiB')

        def test_1_K_plus_1(self):
            # It's not exactly 1 KiB, so show two decimal places
            self.assertEqual(human_size(1024+1), '1.00 KiB')

        def test_2_K_minus_1(self):
            # It's not quite 2 KiB, so show two decimal places
            self.assertEqual(human_size(2048-1), '1.99 KiB')
            
    unittest.main()