Python dict memory issue

Question

I got an issue about memory on my application when adding a lot object into dict then removing out of dict. But it seem python does not free the allocated memory.

Please see my example code:

from memory_profiler import profile
from twisted.internet import reactor


class MyClass(object):
    def __init__(self):
        n = 10
        self.my_array = [[[0 for k in xrange(n)] for j in xrange(n)] for i in xrange(n)]

class TestClass(object):
    token_names = dict()
    counter = 0

    def add(self):
        self.counter = self.counter + 1
        self.token_names[str(self.counter)] = MyClass()


    def testrun(self):
        while True:
            if self.counter > 1000:
                self.remove()
                break
            self.add()

    @profile
    def remove(self):
        print("Remove " + str(len(self.token_names)))
        for k, v in self.token_names.items():
            del self.token_names[k]
        self.token_names.clear()

    @profile
    def start(self):
        self.testrun()


def main():
    test = TestClass()
    test.start()
    reactor.run()


if __name__ == '__main__':
    raise SystemExit(main())

When running this test, the memory growing up and does not free even the dict items were deleted from the dict after finish

But, if I modify the add() function to delete the newly added item from the dict likes that:

def add(self):
    self.counter = self.counter + 1
    self.token_names[str(self.counter)] = MyClass()
    del self.token_names[str(self.counter)]

The memory does not increase in this test.

So, I don't know if I'm missing anything in this example or anything is wrong?

Can you all please help me on this?