Update type check

Signed-off-by: Beat Buesser <[email protected]>

Author: Beat Buesser

art/estimators/estimator.py

@@ -74,6 +74,7 @@ def __init__(
         """
         from art.defences.postprocessor.postprocessor import Postprocessor
         from art.defences.preprocessor.preprocessor import Preprocessor
+
         self._model = model
         self._clip_values = clip_values
 
@@ -120,6 +121,9 @@ def get_params(self) -> Dict[str, Any]:
         return params
 
     def _check_params(self) -> None:
+        from art.defences.postprocessor.postprocessor import Postprocessor
+        from art.defences.preprocessor.preprocessor import Preprocessor
+
         if self._clip_values is not None:
             if len(self._clip_values) != 2:
                 raise ValueError(
@@ -135,7 +139,7 @@ def _check_params(self) -> None:
 
         if isinstance(self.preprocessing_defences, list):
             for preproc_defence in self.preprocessing_defences:
-                if not isinstance(preproc_defence, "Preprocessor"):
+                if not isinstance(preproc_defence, Preprocessor):
                     raise ValueError(
                         "All preprocessing defences have to be instance of "
                         "art.defences.preprocessor.preprocessor.Preprocessor."
@@ -149,7 +153,7 @@ def _check_params(self) -> None:
             )
         if isinstance(self.postprocessing_defences, list):
             for postproc_defence in self.postprocessing_defences:
-                if not isinstance(postproc_defence, "Postprocessor"):
+                if not isinstance(postproc_defence, Postprocessor):
                     raise ValueError(
                         "All postprocessing defences have to be instance of "
                         "art.defences.postprocessor.postprocessor.Postprocessor."