Doesn't adding the gc.collect() just force the garbage collector to run right now instead of waiting until some usage threshold is crossed and then it runs to do the cleanup at some time in the future. Any accumulation of heap use until gc gets around to running isn't really a leak, it is just uncollected garbage. The __del__ doesn't do anything and also doesn't force a gc.collect() by its presence.
http://www.algorithm.co.il/blogs/programming/python-gotchas-1-__del__-is-not-the-opposite-of-__init__/
