CLI progress output (for Bytes) when partial and total may be queried

gistfile1.py

import math
    
    def update(partial, total):
        measurement_heuristic = int(math.floor(math.log10(total)) - 1)/3
        unit, divisor = {
            0: ('B', 1),
            1: ('kB', 1000),
            2: ('MB', 1e6),
            3: ('GB', 1e9),
            4: ('TB', 1e12)
        }[measurement_heuristic]
        print("{0:0.2f}{2} of {1:0.2f}{2} downloaded".format(
                partial/divisor,
                total/divisor,
                unit))