def calculator():
    print("Simple Python Calculator")
    print("Choose an operation:")
    print("1. Addition (+)")
    print("2. Subtraction (-)")
    print("3. Multiplication (*)")
    print("4. Division (/)")

    choice = input("Enter your choice (1/2/3/4): ")

    try:
        num1 = float(input("Enter first number: "))
        num2 = float(input("Enter second number: "))
    except ValueError:
        print("Error: Please enter valid numbers.")
        return

    if choice == "1":
        print("Result:", num1 + num2)
    elif choice == "2":
        print("Result:", num1 - num2)
    elif choice == "3":
        print("Result:", num1 * num2)
    elif choice == "4":
        if num2 == 0:
            print("Error: Division by zero is not allowed.")
        else:
            print("Result:", num1 / num2)
    else:
        print("Invalid choice.")

calculator()