fix possible memory leak associated with Catboost Pool object

freqtrade/freqai/prediction_models/BaseRegressionModel.py

@@ -18,7 +18,7 @@ class BaseRegressionModel(IFreqaiModel):
     such as prediction_models/CatboostPredictionModel.py for guidance.
     """
 
-    def return_values(self, dataframe: DataFrame, dk: FreqaiDataKitchen) -> DataFrame:
+    def return_values(self, dataframe: DataFrame) -> DataFrame:
         """
         User uses this function to add any additional return values to the dataframe.
         e.g.

freqtrade/freqai/prediction_models/BaseTensorFlowModel.py

@@ -16,7 +16,7 @@ class BaseTensorFlowModel(IFreqaiModel):
     User *must* inherit from this class and set fit() and predict().
     """
 
-    def return_values(self, dataframe: DataFrame, dk: FreqaiDataKitchen) -> DataFrame:
+    def return_values(self, dataframe: DataFrame) -> DataFrame:
         """
         User uses this function to add any additional return values to the dataframe.
         e.g.

freqtrade/freqai/prediction_models/CatboostPredictionModel.py

@@ -1,6 +1,6 @@
 import logging
 from typing import Any, Dict
-
+import gc
 from catboost import CatBoostRegressor, Pool
 
 from freqtrade.freqai.prediction_models.BaseRegressionModel import BaseRegressionModel
@@ -42,8 +42,11 @@ class CatboostPredictionModel(BaseRegressionModel):
             **self.model_training_parameters,
         )
 
-        if self.freqai_info.get('data_split_parameters', {}).get('test_size', 0.1) == 0:
-            test_data = None
         model.fit(X=train_data, eval_set=test_data)
 
+        # some evidence that catboost pools have memory leaks:
+        # https://github.com/catboost/catboost/issues/1835
+        del train_data, test_data
+        gc.collect()
+
         return model