def calc(expr: str) -> float:
    a, operation, b = expr.split(" ")
    match operation:
        case "+":
            return float(a) + float(b)
        case "-":
            return float(a) - float(b)
        case "*":
            return float(a) * float(b)
        case "/":
            return float(a) / float(b)
        case _:
            raise ValueError("Не корректная опперация")


result1 = calc(expr="12 + 7")
result2 = calc(expr="50 * 10")
print(result1, result2)