Fixed version of Bryan_Rch’s answer:
def format_bytes(size):
# 2**10 = 1024
power = 2**10
n = 0
power_labels = {0 : '', 1: 'kilo', 2: 'mega', 3: 'giga', 4: 'tera'}
while size > power:
size /= power
n += 1
return size, power_labels[n]+'bytes'