[Python] When creating a list with unique elements from a list with duplicated elements, why...

I want to create a list unique_list that has elements from my_list without the duplicates.

Output should be:

if my_list = [1, 2, 1, 5, 2, 4, 3, 7, 2, 5]
then unique_list = [1, 2, 5, 4, 3, 7]


The code I tried using:

unique_list = []
unique_list = [element for element in my_list if element not in unique_list]


This didn't work and it created a unique_list with all the duplicate elements included (basically a copy of my_list)

I have already found a solution:

unique_list = []
[unique_list.append(element) for element in my_list if not (element in unique_list)]


And this solution:

for element in my_list:
if element not in unique_list:
unique_list.append(element)


I'm trying to understand why using the target list in a list comprehension's condition doesn't work.

Since the for loop solution works, I thought "translating" it into a list comprehension would also work, but it doesn't.

Why does it only work when using .append after defining the list but not when defining unique_list with list comprehension? And why does using the target list unique_list in the for loop condition work but not when using it in the list comprehension condition?

The thing that I tried to do to understand this (after learning that list comprehensions don't leak elements into the enclosing scope) is

unique_list = [5]
unique_list = [element for element in my_list if element not in unique_list]


By assigning 5 to unique_list, the new unique_list won't include any 5s from my_list. So that means the condition in the list comprehension checks if elements are in the old unique_list (the one containing 5). So does list comprehension not use the target list unique_list as it's being updated?

This is how I visualize the list creation process with the two solutions that worked:

element '5' is not in unique_list ([])
element '5' is added to unique_list

element '2' is not in unique_list ([5])
element '2' is added to unique_list

element '7' is not in unique_list ([5, 2])
element '7' is added to unique_list

element '5' is already in unique_list ([5, 2, 7])
element '5' is not added to unique_list

final result: unique_list = [5, 2, 7]


Is this not the case for list comprehension that uses the target list?

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