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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def memory_used(self):
 """To know the allocated memory at function termination. ..versionadded:: 4.1 This property might return None if the function is still running. This function should help to show memory leaks or ram greedy code. """

        if self._end_memory:
            memory_used = self._end_memory - self._start_memory
            return memory_used
        else:
            return None