reflect optuna#809 (comment)

optuna/pruners/hyperband.py

@@ -122,7 +122,10 @@ def _create_bracket_study(self, study, bracket_index):
         # But for safety, prohibit the other attributes explicitly.
         class _BracketStudy(Study):
 
-            _VALID_ATTRS = ('get_trials', 'direction', '_storage')
+            _VALID_ATTRS = (
+                'get_trials', 'direction', '_storage', '_study_id',
+                'pruner', 'study_name', '_bracket_id'
+            )
 
             def __init__(self, study, bracket_id):
                 # type: (Study, int) -> None
@@ -150,6 +153,6 @@ def __getattribute__(self, attr_name):  # type: ignore
                 if attr_name not in _BracketStudy._VALID_ATTRS:
                     raise NotImplementedError
                 else:
-                    return getattr(self, attr_name)
+                    return object.__getattribute__(self, attr_name)
 
         return _BracketStudy(study, bracket_index)

tests/pruners_tests/test_hyperband.py

@@ -51,5 +51,27 @@ def test_bracket_study():
     study = optuna.study.create_study(pruner=pruner)
     bracket_study = pruner._create_bracket_study(study, 0)
 
-    with pytest.raises(Exception):
+    with pytest.raises(NotImplementedError):
         bracket_study.optimize(lambda *args: 1.0)
+
+    for attr in ('set_user_attr', 'set_system_attr'):
+        with pytest.raises(NotImplementedError):
+            getattr(bracket_study, attr)('abc', 100)
+
+    for attr in ('user_attrs', 'system_attrs'):
+        with pytest.raises(NotImplementedError):
+            getattr(bracket_study, attr)
+
+    with pytest.raises(Exception):
+        bracket_study.trials_dataframe()
+
+    bracket_study.get_trials()
+    bracket_study.direction
+    bracket_study._storage
+    bracket_study._study_id
+    bracket_study.pruner
+    bracket_study.study_name
+    # As `_BracketStudy` is defined inside `HyperbandPruner`,
+    # we cannot do `assert isinstance(bracket_study, _BracketStudy)`.
+    # This is why the below line is ignored by mypy checks.
+    bracket_study._bracket_id  # type: ignore