python/exercises/variable-length-quantity/example.py

EIGHTBITMASK = 0x80
SEVENBITSMASK = 0x7f


def encode_single(n):
    bytes_ = [n & SEVENBITSMASK]
    n >>= 7

    while n > 0:
        bytes_.append(n & SEVENBITSMASK | EIGHTBITMASK)
        n >>= 7

    return bytes_[::-1]


def encode(numbers):
    return sum((encode_single(n) for n in numbers), [])


def decode(bytes_):
    values = []
    n = 0

    for i, byte in enumerate(bytes_):
        n <<= 7
        n += (byte & SEVENBITSMASK)

        if byte & EIGHTBITMASK == 0:
            values.append(n)
            n = 0
        elif i == len(bytes_) - 1:
            raise ValueError('incomplete byte sequence')

    return values