hex_to_decimal.py

'''
Simple example on how to manually convert hex to decimal without using
'int()' method.
'''
from functools import reduce


def to_decimal(hexnr):
    assert hexnr.startswith('0x')

    hextable = {'a': 10, 'b': 11, 'c': 12, 'd': 13, 'e': 14, 'f': 15}

    hexnr = hexnr.lower()

    return reduce(lambda a, b: (a[1] if isinstance(a, tuple) else a) + b[1] * pow(16, b[0]),
                  [(i, int(hextable[c] if c in hextable else c) if i < len(hexnr) - 2 else 0)
                   for i, c in enumerate(hexnr[::-1])])


hexnr = '0x303e'

a = to_decimal(hexnr)
print(a)

b = int(hexnr, 16)
print(b)

assert a == b