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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_fetcher_assets(self, dt):
 """ Returns a list of assets for the current date, as defined by the fetcher data. Returns ------- list: a list of Asset objects. """

        # return a list of assets for the current date, as defined by the
        # fetcher source
        if self._extra_source_df is None:
            return []

        day = normalize_date(dt)

        if day in self._extra_source_df.index:
            assets = self._extra_source_df.loc[day]['sid']
        else:
            return []

        if isinstance(assets, pd.Series):
            return [x for x in assets if isinstance(x, Asset)]
        else:
            return [assets] if isinstance(assets, Asset) else []