def add(x, y): return x + y
def subtract(x, y): return x - y
def multiply(x, y): return x * y
def divide(x, y): return x / y if y != 0 else "Error: Division by zero"

print("--- Python Calculator ---")
print("Select operation: 1.Add, 2.Subtract, 3.Multiply, 4.Divide")

while True:
    choice = input("Enter choice (1/2/3/4) or 'q' to quit: ")

    if choice.lower() == 'q':
        break

    if choice in ('1', '2', '3', '4'):
        num1 = float(input("Enter first number: "))
        num2 = float(input("Enter second number: "))

        if choice == '1':
            print(f"{num1} + {num2} = {add(num1, num2)}")
        elif choice == '2':
            print(f"{num1} - {num2} = {subtract(num1, num2)}")
        elif choice == '3':
            print(f"{num1} * {num2} = {multiply(num1, num2)}")
        elif choice == '4':
            print(f"{num1} / {num2} = {divide(num1, num2)}")
    else:
        print("Invalid Input")