Not sure if this is the desired behavior but wanted to bring it up anyways.
When you have a class and have a variable in like:
class TestClass(object):
    variable = []

then you run it through a loop like:
for num in range(10):
    test = TestClass()
    test.variable.append(num)

even if you assign another variable to it or none like:
test = "blah"
test = None

then reassign the class:
test = TestClass()
print(test.variable)

will return all the numbers in the list.
also doesn't seem to matter if garbage collection was manually ran.

Attached is a small example code.
This was found on Macos and tested with both python 3.7 and 2.7 Subsequently same on ubuntu with python 3.5 and python 2.7