Formatting bytes intelligently with Python

import math

def format_bytes(n):

    units = ('', 'KiB', 'MiB', 'GiB', 'TiB', 'PiB')
    base = 1024
    decrement_threshold = 0.2
    divisor_max = len(units) - 1

    exponent = math.log(n, base) if n > 0 else 0
    remainder = exponent % 1
    exponent = int(exponent)  # implicit floor

    decrement = int(0 < remainder < decrement_threshold)
    divisor = max(0, exponent - decrement)
    divisor = min(divisor, divisor_max)

    quotient = int(n/(base**divisor))  # implicit floor
    unit = units[divisor]
    return "{} {}".format(quotient, unit)