#!/usr/bin/env python
import argparse, sys
parser = argparse.ArgumentParser(description="Format numbers as human readable byte units. Accepts basic mathematical expressions. Characters allowed are \"0123456789\\t\\n -+/*%\".")
parser.add_argument("bytes", help="number to format")
parser.add_argument("--no-suffix", help="don't add a 'B' suffix to the end of the output", action="store_true")
args = parser.parse_args()
allowed_chars = '0123456789\t\n -+/*%'

def format(num):
    suffix = 'B'
    units = ['', 'K', 'M', 'G', 'T', 'P', 'E', 'Z']
    if args.no_suffix:
        suffix = ''
        units = ['B', 'K', 'M', 'G', 'T', 'P', 'E', 'Z']

    for unit in units:
        if abs(num) < 1024.0:
            return "%3.1f%s%s" % (num, unit, suffix)
        num /= 1024.0
    return "%.1f%s%s" % (num, 'Yi', suffix)


for char in args.bytes:
    if char not in allowed_chars:
        sys.stderr.write("{}: error: argument bytes: invalid int value or math expression: '{}'\n".format("formatbytes", args.bytes))
        sys.exit(1)

try:
    evaluated = eval(args.bytes)
except SyntaxError:
    sys.stderr.write("{}: error: argument bytes: error while evaluating expression: '{}'\n".format("formatbytes", args.bytes))
    sys.exit(1)

print(format(evaluated))