Python 3 program about finding the average of integers in a list

Question

list1 = []

while True:
    num=input("enter a number or input q to quit or input a for the average\n")
    if isinstance(num, int):
        list1.append(num)
    elif isinstance(num, str):
        if num == "q":
            exit()
        elif num == "a":
            print(list1)
        else:
            print("stop")

I'm a python beginner, and I've made this program to find the average of integers in a list, but for some reason it does not add any integers to the list. I don't know why it doesn't work