src/transformers/models/auto/configuration_auto.py/_LazyConfigMapping/__getitem__
class _LazyConfigMapping:    def __getitem__(self, key):
        if key not in self._mapping:
            raise KeyError(key)
        value = self._mapping[key]
        module_name = model_type_to_module_name(key)
        if module_name not in self._modules:
            self._modules[module_name] = importlib.import_module(f".{module_name}", "transformers.models")
        return getattr(self._modules[module_name], value)