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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 strip_unknown_features(self):
 """ Remove features not found in the `gffutils.FeatureDB`. This will typically include 'ambiguous', 'no_feature', etc, but can also be useful if the database was created from a different one than was used to create the table. """

        if not self.db:
            return self
        ind = []
        for i, gene_id in enumerate(self.data.index):
            try:
                self.db[gene_id]
                ind.append(i)
            except gffutils.FeatureNotFoundError:
                pass
        ind = np.array(ind)
        return self.__class__(self.data.ix[ind], **self._kwargs)