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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 load_hdf(cls, filename, path=''):
 """Loads OrbitPopulation from HDF file. :param filename: HDF file :param path: Path within HDF file store where :class:`OrbitPopulation` is saved. """

        df = pd.read_hdf(filename,'{}/df'.format(path))
        return cls.from_df(df)