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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 _fill(self):
 """Fills bucket with accrued tokens since last fill."""


        right_now = time.time()
        time_diff = right_now - self._last_fill
        if time_diff < 0:
            return

        self._count = min(
            self._count + self._fill_rate * time_diff,
            self._capacity,
        )
        self._last_fill = right_now