import math

def convertBytes(bytes, lst=None):
    if lst is None:
        lst=['Bytes', 'KB', 'MB', 'GB', 'TB', 'PB']
    i = int(math.floor( # 舍弃小数点，取小
             math.log(bytes, 1024) # 求对数(对数：若 a**b = N 则 b 叫做以 a 为底 N 的对数)
            ))

    if i >= len(lst):
        i = len(lst) - 1
    return ('%.2f' + " " + lst[i]) % (bytes/math.pow(1024, i))