base32 encoder/decoder

base32

#!/usr/bin/env python
"""base32 encoding based on http://www.crockford.com/wrmg/base32.html

Encodes the positive integer on stdin. This tool is designed to parallel
base64(1).

Usage: base32 [-h | -D]
  -h  print this help
  -D  decode input instead
"""

import sys

CHARS = "0123456789ABCDEFGHJKMNPQRSTVWXYZ"


def encode(num):
    if num <= 0:
        sys.stderr.write('num must be greater than 0\n')
        sys.exit(1)

    encoded_chars = []
    while num > 0:
        remainder = num % 32
        num //= 32
        encoded_chars.append(CHARS[remainder])
    return ''.join(encoded_chars[::-1])


def decode(string):
    string = clean(string)
    num = 0
    for power, char in enumerate(string[::-1]):
        try:
            val = CHARS.index(char)
        except ValueError:
            raise ValueError('invalid character: %s' % char)
        num += 32 ** power * val
    return num


def clean(string):
    # Hyphens are allowed:
    string = string.replace('-', '')
    # Case insensitive:
    string = string.upper()
    # Ambiguous chars:
    string = string.replace('I', '1').replace('L', '1')
    string = string.replace('O', '0')
    return string


def usage():
    sys.stderr.write(str(__doc__))


if __name__ == '__main__':
    if len(sys.argv) > 1 and sys.argv[1] == '-h':
        usage()
        sys.exit(0)

    if len(sys.argv) > 1 and sys.argv[1] == '-D':
        print decode(sys.stdin.read().strip())
    else:
        print encode(int(sys.stdin.read()))