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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 from_file(cls, h5_file):
 """ Construct from an h5py.File. Parameters h5_file : h5py.File An HDF5 daily pricing file. """

        return cls({
            country: HDF5DailyBarReader.from_file(h5_file, country)
            for country in h5_file.keys()
        })