add_snafu.py

VALUES = {"2": 2, "1": 1, "0": 0, "-": -1, "=": -2}
LETTERS = {2: "2", 1: "1", 0: "0", -1: "-", -2: "="}

def add_snafu(left: str, right: str) -> str:
    carry = 0

    left_list, right_list = list(left), list(right)

    sum = []

    while left_list or right_list or carry:
        try:
            left_value = VALUES[left_list.pop()]
        except IndexError:
            left_value = 0
        try:
            right_value = VALUES[right_list.pop()]
        except IndexError:
            right_value = 0
    
        value = left_value + right_value + carry
        if value > 2:
            value -= 5
            carry = 1
        elif value < -2:
            value += 5
            carry = -1
        else:
            carry = 0

        sum.append(value)
    
    return "".join([LETTERS[value] for value in sum[::-1]])