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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 duration_so_far(self):
 """Return how the duration so far. :returns: the duration from the time the Interval was started if the interval is running, otherwise ``False``. """

        if self._start_instant is None:
            return False
        if self._stop_instant is None:
            return int((instant() - self._start_instant) * 1000)
        return False