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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_input(self, name, ds):
 """ Retrieves the content of an input given a DataSource. The input acts like a filter over the outputs of the DataSource. Args: name (str):
 The name of the input. ds (openflow.DataSource):
 The DataSource that will feed the data. Returns: pandas.DataFrame: The content of the input. """

        columns = self.inputs.get(name)
        df = ds.get_dataframe()

        # set defaults
        for column in columns:
            if column not in df.columns:
                df[column] = self.defaults.get(column)

        return df[columns]