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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 universe(self):
 """ Data universe available at the current time. Universe contains the data passed in when creating a Backtest. Use this data to determine strategy logic. """

        # avoid windowing every time
        # if calling and on same date return
        # cached value
        if self.now == self._last_chk:
            return self._funiverse
        else:
            self._last_chk = self.now
            self._funiverse = self._universe.loc[:self.now]
            return self._funiverse