decompress

#!/usr/bin/env python3

import argparse
import math
import sys

int_size = sys.getsizeof(int())
methods = ['binary', 'unary', 'gamma', 'delta']

def parse_args():
    parser = argparse.ArgumentParser(description='Decompress an integer.')
    parser.add_argument('method', metavar='M', type=str, nargs=1, choices=methods, help='the encoding method used')
    parser.add_argument('compressed', metavar='C', type=str, nargs=1, help='the encoded integer to decode')
    return parser.parse_args()

"""
Simply convert from binary to decimal.
"""
def binary_decompression(compressed):
    try:
        return int(compressed, 2)
    except ValueError:
        sys.exit('Invalid binary encoding: \"' + compressed + '\"')

"""
Count the number of ones until reaching a zero.
"""
def unary_decompression(compressed):
    num_ones = 0
    for bit in compressed:
        if bit == '1':
            num_ones = num_ones + 1
        elif bit == '0':
            if len(compressed) != num_ones + 1:
                sys.exit('Invalid unary encoding: \"' + compressed + '\"')
            return num_ones + 1
        else:
            sys.exit('Invalid unary encoding: \"' + compressed + '\"')
    sys.exit('Invalid unary encoding: \"' + compressed + '\"')

"""
First decode the unary part and call it k+1. Then read k more bits, decode it as binary, and call it r.
The final value is (2^k)+r
"""
def gamma_decompression(compressed):
    zero_loc = compressed.index('0')
    k = unary_decompression(compressed[:zero_loc + 1]) - 1
    r = binary_decompression(compressed[zero_loc + 1:zero_loc + 1 + k])
    return int(math.pow(2, k)) + r

"""
First decode the unary part of the gamma part and call it k+1. Then read k more bits, decode it as binary
and call it r. The value of the gamma part is (2^k)+r, call it m+1. Then read m more bits, decode it as
binary and call it s. The final value is (2^m)+s.
"""
def delta_decompression(compressed):
    zero_loc = compressed.index('0')
    k = unary_decompression(compressed[:zero_loc + 1]) - 1
    r = binary_decompression(compressed[zero_loc + 1:zero_loc + 1 + k])
    m = (int(math.pow(2, k)) + r) - 1
    s = binary_decompression(compressed[zero_loc + 1 + k:zero_loc + 1 + k + m])
    return int(math.pow(2, m)) + s

def main():
    args = parse_args()
    compressed = args.compressed[0]
    method = args.method[0]
    if method == 'binary':
        print(binary_decompression(compressed))
    elif method == 'unary':
        print(unary_decompression(compressed))
    elif method == 'gamma':
        print(gamma_decompression(compressed))
    elif method == 'delta':
        print(delta_decompression(compressed))
    else:
        sys.exit('Unimplemented compression method: \"' + method + '\"')

if __name__ == '__main__':
    main()