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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(cls, folder):
 """ Loads PopulationSet from folder ``popset.h5`` and ``trsig.pkl`` must exist in folder. :param folder: Folder from which to load. """

        popset = PopulationSet.load_hdf(os.path.join(folder,'popset.h5'))
        sigfile = os.path.join(folder,'trsig.pkl')
        with open(sigfile, 'rb') as f:
            trsig = pickle.load(f)
        return cls(trsig, popset, folder=folder)