Base58 decoder

base58.py

#!/usr/bin/env python2.7

import sys
import os
import argparse

# Base58 charset
alphabet = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz'


if bytes == str:  # python2
    iseq = lambda s: map(ord, s)
    bseq = lambda s: ''.join(map(chr, s))
    buffer = lambda s: s

def b58encode(v):

    origlen = len(v)
    v = v.lstrip(b'\0')
    newlen = len(v)

    p, acc = 1, 0
    for c in iseq(v[::-1]):
        acc += p * c
        p = p << 8

    result = ''
    while acc > 0:
        acc, mod = divmod(acc, 58)
        result += alphabet[mod]

    return (result + alphabet[0] * (origlen - newlen))[::-1]


def b58decode(v):

    if not isinstance(v, str):
        v = v.decode('ascii')

    origlen = len(v)
    v = v.lstrip(alphabet[0])
    newlen = len(v)

    p, acc = 1, 0
    for c in v[::-1]:
        try:
            acc += p * alphabet.index(c)
            p *= 58
        except:
            continue

    result = []
    while acc > 0:
        acc, mod = divmod(acc, 256)
        result.append(mod)

    return (bseq(result) + b'\0' * (origlen - newlen))[::-1]


def main():
    parser = argparse.ArgumentParser(description="Byte converter")
    parser.add_argument('--decode', dest="decode", default=False, help="Decode?", action='store_true')
    parser.add_argument('--infile', dest="infile", default=None, help="Input file", required=True)
    parser.add_argument('--outfile', dest="outfile", default="out.tmp", help="Output file")
    args = parser.parse_args()

    outbuf = None
    with open(args.infile, "r") as fileIn:
        buf = fileIn.read()
        if args.decode:
            outbuf = b58decode(buf)
        else:
            outbuf = b58encode(buf)
    if outbuf == None:
        print "Failed"
        return

    with open(args.outfile, "wb") as fileOut:
        fileOut.write(outbuf)
        print "Saved to a file: " + args.outfile


if __name__ == "__main__":
    sys.exit(main())