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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 model_function(self, model_name, version, func_name):
 """Return the model-specific caching function."""

        assert func_name in ('serializer', 'loader', 'invalidator')
        name = "%s_%s_%s" % (model_name.lower(), version, func_name)
        return getattr(self, name)