Q:

How do I generate random but unique numbers in python?

I want to generate a random number, and that random number should be unique, meaning it should not be repeated or generated again. I have tried making a list where I append in every iteration and check if it is already present in the list or not. If it is present in the list, the number is not appended. But I don't think it is an effective method. So, please help me with it.
    import random
    #an empty list to append randomly generated numbers
    empty = []
    while True:
        #checking from range 500 to 510
        number = random.randrange(500, 510)
        if number not in empty:
            empty.append(number)
        else:
            pass
        #breaking the loop if the length of the numbers is 9
        if len(empty) == 9:
            break

    print("Final list --> " + str(empty))

A:

You can get such a list of a given number of non-repeating elements taken from a given pool via random.sample:
>>> random.sample(range(500, 510), 9)
[500, 501, 503, 502, 505, 507, 508, 506, 504]

