Problem with filtering data via custom function in Python (Django)

I want to get 4 random objects from Product I’m trying to filter it by check_existing_id function and random.randint and I use while loop to get 4 objects from the database. However this piece of code in some cases returns only 3 objects. There is a bug hidden in the code and I have no idea where I need this to return exacly 4 elements every single time. I’m pasting the code below it’s just a simple function:

def check_existing_id(list,number):
        for i in range(len(list)):
            if list[i] == number:
                return False
        return True

class GetRecommendedProducts(generics.ListAPIView):
    serializer_class = ProductSerializer
    
    def get_queryset(self):
        product_id = self.kwargs['product_id']
        products_length = len(Product.objects.all())
        id_list = []
        while len(id_list) < 4:
            id = random.randint(0, products_length)
            if check_existing_id(id_list, id) and id != product_id:
                id_list.append(id)

        return Product.objects.filter(id__in=id_list)

>Solution :

You can make use of the sample(…) function [Python-doc] of the random package [Python-doc]. You can first fetch the list of primary keys (excluding the product_id), then sampling four items, and then fetch the Products:

from random import sample

class GetRecommendedProducts(generics.ListAPIView):
    serializer_class = ProductSerializer
    
    def get_queryset(self):
        id_list = list(Product.objects.exclude(
            id=self.kwargs['product_id']
        ).values_list('id', flat=True))
        return Product.objects.filter(id__in=sample(id_list, 4))