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