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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 parallactic_angles(self, context):
 """ parallactic angle data source """

        # Time and antenna extents
        (lt, ut), (la, ua) = context.dim_extents('ntime', 'na')

        return (mbu.parallactic_angles(self._times[lt:ut],
                self._antenna_positions[la:ua], self._phase_dir)
                                            .reshape(context.shape)
                                            .astype(context.dtype))