import unittest
import gc

class TestGC(unittest.TestCase):
    def test_zip(self):
        container = []
        iterator = zip([container], [container])

        # untrack the internal zip->result=(None, None)
        gc.collect()

        # create a reference cycle: container -> iterator -> container
        container.append(iterator)

        next(iterator)
        # zip->result=(container, container)

        del container, iterator

        # Try to break the reference cycle
        gc.collect()