Change returned model in get_model of BATSModel, TBATSModel (#987)

CHANGELOG.md

@@ -18,7 +18,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 -
 ### Changed
 -
--
+- Change returned model in get_model of BATSModel, TBATSModel ([#987](https://github.com/tinkoff-ai/etna/pull/987))
 - 
 - 
 - 

etna/models/tbats.py

@@ -16,7 +16,7 @@
 
 class _TBATSAdapter(BaseAdapter):
     def __init__(self, model: Estimator):
-        self.model = model
+        self._model = model
         self._fitted_model: Optional[Model] = None
         self._last_train_timestamp = None
         self._freq = None
@@ -27,7 +27,7 @@ def fit(self, df: pd.DataFrame, regressors: Iterable[str]):
             raise ValueError("Can't determine frequency of a given dataframe")
 
         target = df["target"]
-        self._fitted_model = self.model.fit(target)
+        self._fitted_model = self._model.fit(target)
         self._last_train_timestamp = df["timestamp"].max()
         self._freq = freq
 
@@ -68,8 +68,15 @@ def predict(self, df: pd.DataFrame, prediction_interval: bool, quantiles: Iterab
 
         return y_pred
 
-    def get_model(self) -> Estimator:
-        return self.model
+    def get_model(self) -> Model:
+        """Get internal :py:class:`tbats.tbats.Model` model that was fitted inside etna class.
+
+        Returns
+        -------
+        :
+           Internal model
+        """
+        return self._fitted_model
 
 
 class BATSModel(PerSegmentPredictionIntervalModel):