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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 get_orderbook(self):
 """Get orderbook for the instrument :Retruns: orderbook : dict orderbook dict for the instrument """

        if self in self.parent.books.keys():
            return self.parent.books[self]

        return {
            "bid": [0], "bidsize": [0],
            "ask": [0], "asksize": [0]
        }