Unit-Converter as decorator

#!/usr/bin/env python3
import math
import functools
import argparse
import sys

def convert(func):
    units = ['B', 'KiB', 'MiB', 'GiB', 'TiB', 'PiB', 'EiB', 'ZiB', 'YiB']
    @functools.wraps(func)
    def inner(*args, **kwargs):
        size = func(*args, **kwargs)
        index = int(math.log(size, 1024))
        div = math.pow(1024, index)
        try:
            return '{:.2f} {}'.format(size/div, units[index])
        except IndexError:
            return '{:.2f} * 2^{} Byte'.format(size/div, index*10)
    return inner

@convert
def get_size(size):
    return size

if __name__ == '__main__':
    if not sys.stdin.isatty():
        size = int(sys.stdin.read())
    else:
        parser = argparse.ArgumentParser(description='Convert from Bytes')
        parser.add_argument('size', type=int, help='size to convert')
        args = parser.parse_args()
        size = args.size
    print(get_size(size))