equation-solver-kata.py

operands = {
    '+': lambda a, b: a + b,
    '-': lambda a, b: a - b,
    'x': lambda a, b: a * b,
    '/': lambda a, b: a / b
}


def parse(eq):
    bits = []
    last_num = ''
    for index in range(len(eq)):
        char = eq[index]
        if char.isdigit():
            last_num += char
        elif char == ' ':
            continue
        elif char in operands:
            bits.append(last_num)
            bits.append(char)
            last_num = ''
    if last_num != '':
        bits.append(last_num)
    return bits


def solve(eq):
    result = 0
    last_operand = operands['+']
    for bit in parse(eq):
        if bit.isdigit():
            result = last_operand(result, int(bit))
        else:
            last_operand = operands[bit]
    return result

if __name__ == '__main__':
    assert solve('0') == 0
    assert solve('1') == 1
    assert solve('1 + 1') == 2
    assert solve('1 + 1 x 5') == 10
    assert solve('1 + 1 x 5 + 6') == 16
    assert solve('1 + 1 x 5 + 6 / 4') == 4
    assert solve('1 + 1 x 5 + 6 / 4 + 8') == 12