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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 retrieve_data(self):
 """ Retrives data as a DataFrame. """


        #==== Retrieve data ====#

        df = self.manager.get_historic_data(self.start.date(), self.end.date())
        df.replace(0, np.nan, inplace=True)
        return df