1👍
I don’t know why do you receive duplicate results, because i don’t see nothing unnatural in your code.
In case if you want just to receive a list of cars id (without duplicates), you can change your for cycle in this way:
cars_id = [] # creating empty list for cars id with duplicates
for car in cars: # for cycle
cars_id.append(car.id) # appends numbers 3, 3, 3, 5 to our list
cars_id = list(set(cars_id)) # making list with unique values using built-in function set()
So after you’ll have something like this:
>>> cars_id
... [3, 5]
Source:stackexchange.com