A list of lists

[Hassediagram]

As Larz said, this functionality is all covered in Python. But if you need to recreate it for homework, to get the subsets, start with a list of the empty set. Loop through the items in the set, adding to the list of subsets every subset plus the item:

>>> subsets = [[]]
>>> fullset = [1, 2, 3]
>>> for item in fullset:
...    subsets = subsets + [subset + [item] for subset in subsets]
...
>>> subsets
[[], [1], [2], [1, 2], [3], [1, 3], [2, 3], [1, 2, 3]]

You should be able to modify that to get the list of subsets you want.

Thank you ichabod801, this works ! I will use your trick.
But why didn't it work in my program ?

Thank you also for your suggestion about the intersections.