Sanitize argument-free object params before logging (#19771)

Co-authored-by: awaelchli <aedu.waelchli@gmail.com>

src/lightning/fabric/CHANGELOG.md

@@ -9,6 +9,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 ### Added
 
+- Added sanitization for classes before logging them as hyperparameters ([#19771](https://github.com/Lightning-AI/pytorch-lightning/pull/19771))
+
 - Enabled consolidating distributed checkpoints through `fabric consolidate` in the new CLI ([#19560](https://github.com/Lightning-AI/pytorch-lightning/pull/19560))
 
 - Added the ability to explicitly mark forward methods in Fabric via `_FabricModule.mark_forward_method()` ([#19690](https://github.com/Lightning-AI/pytorch-lightning/pull/19690))

src/lightning/fabric/utilities/logger.py

@@ -11,6 +11,8 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+
+import inspect
 import json
 from argparse import Namespace
 from dataclasses import asdict, is_dataclass
@@ -52,8 +54,11 @@ def _sanitize_callable_params(params: Dict[str, Any]) -> Dict[str, Any]:
     """
 
     def _sanitize_callable(val: Any) -> Any:
-        # Give them one chance to return a value. Don't go rabbit hole of recursive call
+        if inspect.isclass(val):
+            # If it's a class, don't try to instantiate it, just return the name
+            return val.__name__
         if callable(val):
+            # Callables get a chance to return a name
             try:
                 _val = val()
                 if callable(_val):

tests/tests_fabric/utilities/test_logger.py

@@ -92,7 +92,7 @@ class B:
 
 
 def test_sanitize_callable_params():
-    """Callback function are not serializiable.
+    """Callback functions are not serializable.
 
     Therefore, we get them a chance to return something and if the returned type is not accepted, return None.
 
@@ -104,11 +104,21 @@ def return_something():
     def wrapper_something():
         return return_something
 
+    class ClassNoArgs:
+        def __init__(self):
+            pass
+
+    class ClassWithCall:
+        def __call__(self):
+            return "name"
+
     params = Namespace(
         foo="bar",
         something=return_something,
         wrapper_something_wo_name=(lambda: lambda: "1"),
         wrapper_something=wrapper_something,
+        class_no_args=ClassNoArgs,
+        class_with_call=ClassWithCall,
     )
 
     params = _convert_params(params)
@@ -118,6 +128,8 @@ def wrapper_something():
     assert params["something"] == "something"
     assert params["wrapper_something"] == "wrapper_something"
     assert params["wrapper_something_wo_name"] == "<lambda>"
+    assert params["class_no_args"] == "ClassNoArgs"
+    assert params["class_with_call"] == "ClassWithCall"
 
 
 def test_sanitize_params():