convert_between_bases.py

#!/usr/bin/env python

def convert_base(value, base_k, base_n):
    """
    Convert value from base K to base N
    >>> convert_base('5', BASE10, BASE2)
    101
    >>> convert_base('10', BASE10, BASE2)
    1010
    >>> convert_base('33', BASE4, BASE8)
    17
    """
    num = express_value_in_base10(value, base_k)
    return express_base10_value_in_base(num, base_n)


def express_value_in_base10(value, base):
    """
    >>> express_value_in_base10('100', BASE10)
    100
    >>> express_value_in_base10('100', BASE2)
    4
    >>> express_value_in_base10('220', BASE3)
    24
    """
    polynoms = get_nb_polynoms_for_base(base, len(value))
    return sum(map(lambda x: base.find(value[x])*polynoms[x], range(len(value))))

def express_base10_value_in_base(value, base):
    """
    >>> express_base10_value_in_base(24, BASE3)
    220
    >>> express_base10_value_in_base(24, BASE8)
    30
    >>> express_base10_value_in_base(24, BASE10)
    24
    >>> express_base10_value_in_base(24, BASE20)
    14
    """
    tar = len(base)
    res = ""
    k = value
    while k != 0:
        k, l = k / tar, k % tar
        res = base[l] + res
    return int(res)

def get_nb_polynoms_for_base(base, nb):
    """
    >>> get_nb_polynoms_for_base(BASE2, 4)
    [8, 4, 2, 1]
    >>> get_nb_polynoms_for_base(BASE3, 5)
    [81, 27, 9, 3, 1]
    """
    return map(lambda x: len(base)**(nb-x-1), range(nb))

def int_to_str(x):
    """
    >>> int_to_str(9)
    '9'
    >>> int_to_str(16)
    'G'
    >>> int_to_str(32)
    'W'
    """
    return str(x) if x < 10 else chr(55 + x)

def base_as_str(base):
    """
    >>> base_as_str(20)
    '0123456789ABCDEFGHIJ'
    >>> base_as_str(30)
    '0123456789ABCDEFGHIJKLMNOPQRST'
    """
    return base if isinstance(base, str) else ''.join(map(int_to_str, range(base)))

BASE10 = base_as_str(10)
BASE2  = base_as_str(2)
BASE3  = base_as_str(3)
BASE4  = base_as_str(4)
BASE8  = base_as_str(8)
BASE12 = base_as_str(12)
BASE20 = base_as_str(20)