Improve warning for unpickable hyperparameter (#19581)

Author: awaelchli

src/lightning/pytorch/utilities/parsing.py

@@ -41,7 +41,10 @@ def clean_namespace(hparams: MutableMapping) -> None:
     del_attrs = [k for k, v in hparams.items() if not is_picklable(v)]
 
     for k in del_attrs:
-        rank_zero_warn(f"attribute '{k}' removed from hparams because it cannot be pickled")
+        rank_zero_warn(
+            f"Attribute '{k}' removed from hparams because it cannot be pickled. You can suppress this warning by"
+            f" setting `self.save_hyperparameters(ignore=['{k}'])`.",
+        )
         del hparams[k]
 
 

tests/tests_pytorch/models/test_hparams.py

@@ -528,19 +528,26 @@ def test_hparams_pickle(tmpdir):
 class UnpickleableArgsBoringModel(BoringModel):
     """A model that has an attribute that cannot be pickled."""
 
-    def __init__(self, foo="bar", pickle_me=(lambda x: x + 1), **kwargs):
+    def __init__(self, foo="bar", pickle_me=(lambda x: x + 1), ignore=False, **kwargs):
         super().__init__(**kwargs)
         assert not is_picklable(pickle_me)
-        self.save_hyperparameters()
+        if ignore:
+            self.save_hyperparameters(ignore=["pickle_me"])
+        else:
+            self.save_hyperparameters()
 
 
 def test_hparams_pickle_warning(tmpdir):
     model = UnpickleableArgsBoringModel()
     trainer = Trainer(default_root_dir=tmpdir, max_steps=1)
-    with pytest.warns(UserWarning, match="attribute 'pickle_me' removed from hparams because it cannot be pickled"):
+    with pytest.warns(UserWarning, match="Attribute 'pickle_me' removed from hparams because it cannot be pickled"):
         trainer.fit(model)
     assert "pickle_me" not in model.hparams
 
+    model = UnpickleableArgsBoringModel(ignore=True)
+    with no_warning_call(UserWarning, match="Attribute 'pickle_me' removed from hparams because it cannot be pickled"):
+        trainer.fit(model)
+
 
 def test_hparams_save_yaml(tmpdir):
     class Options(str, Enum):