Calculator in python

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):
    if y == 0:
        return "Error! Division by zero."
    return x / y

def main():
    print("Welcome to the Simple Calculator!")
    print("Select operation:")
    print("1. Add")
    print("2. Subtract")
    print("3. Multiply")
    print("4. Divide")
    
    while True:
        choice = input("Enter choice (1/2/3/4) or 'q' to quit: ")
        
        if choice == 'q':
            print("Exiting the calculator. Goodbye!")
            break

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