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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 get_or_create_index(cls, app, wh):
 """Gets a previously cached index or creates a new one for the given app and whoosheer. :param app: The application instance. :param wh: The whoosheer instance for which the index should be retrieved or created. """

        if wh in app.extensions['whooshee']['whoosheers_indexes']:
            return app.extensions['whooshee']['whoosheers_indexes'][wh]
        index = cls.create_index(app, wh)
        app.extensions['whooshee']['whoosheers_indexes'][wh] = index
        return index