calculator

[Jei]

i changed sub() to num_1() and num_2()

it works fine untill i use a letter. then i get this error

    print("The result is:", int(num1) - int(num2))
TypeError: int() argument must be a string, a bytes-like object or a number, not 'NoneType'
>>>

import math

print("Calculator")

def num_1():
    try:
        num1 = int(input("Give a number: "))
    except (TypeError, ValueError):        
        print("This input is invalid.")
        num1 = None
        num_1()
    else:
        return num1

def num_2():
    try:
        num2 = int(input("Give a number: "))
    except (TypeError, ValueError):
        print("This input is invalid.")
        num2 = None
        num_2()
    else:
        return num2
        
    
    
    

def main():
    while True:
        num1 = num_1()
        num2 = num_2()
        print("(1)+")
        print("(2)-")
        print("(3)*")
        print("(4)/")
        print("(5)sin(number1/number2)")
        print("(6)cos(number1/number2)")
        print("(7)Change numbers")
        print("(8)Quit")
        print("Current numbers: ", num1, num2)
        num3 = int(input("Please select something (1-6): "))
        if num3 == 1:
            print("The result is:", int(num1) + int(num2))
        elif num3 == 2:
            print("The result is:", int(num1) - int(num2))
        elif num3 == 3:
            print("The result is:", int(num1) * int(num2))
        elif num3 == 4:
            print("The result is:", int(num1) / int(num2))
        elif num3 == 5:
            print("The result is:", (math.sin(int(num1) / int(num2))))
        elif num3 == 6:
            print("The result is:", (math.cos(int(num1) / int(num2))))
        elif num3 == 7:
            num1 = None
            num2 = None
            main()
        elif num3 == 8:
            print("Thank you!")
            break
        else:
            print("Selection was not correct.")

        
if __name__ == "__main__":
    main()