fix: notify users if using incompatible pydantic & python combo

Author: carlos-marchal-ph

posthog/test/test_utils.py

@@ -1,3 +1,4 @@
+import sys
 import time
 import unittest
 from dataclasses import dataclass
@@ -122,11 +123,29 @@ class NestedModel(BaseModel):
             "bar": 2,
             "baz": None,
         }
-        assert utils.clean(ModelV1(foo=1, bar="2")) == {"foo": 1, "bar": "2"}
+        # Pydantic V1 is not compatible with Python 3.14+
+        if sys.version_info < (3, 14):
+            assert utils.clean(ModelV1(foo=1, bar="2")) == {"foo": 1, "bar": "2"}
         assert utils.clean(NestedModel(foo=ModelV2(foo="1", bar=2, baz="3"))) == {
             "foo": {"foo": "1", "bar": 2, "baz": "3"}
         }
 
+    @unittest.skipIf(sys.version_info < (3, 14), "Test only relevant for Python 3.14+")
+    def test_clean_pydantic_v1_warning_on_python_314(self):
+        """Verify that Pydantic V1 models emit a warning on Python 3.14+"""
+        class ModelV1(BaseModelV1):
+            foo: int
+            bar: str
+
+        with self.assertLogs("posthog", level="WARNING") as cm:
+            result = utils.clean(ModelV1(foo=1, bar="2"))
+            # V1 models return empty dict on Python 3.14+
+            assert result == {}
+
+        # Verify the warning was emitted
+        assert len(cm.output) == 1
+        assert "Pydantic V1 models are not compatible with Python 3.14+" in cm.output[0]
+
     def test_clean_pydantic_like_class(self) -> None:
         class Dummy:
             def model_dump(self, required_param: str) -> dict:

posthog/utils.py

@@ -71,10 +71,15 @@ def clean(item):
             item = item.model_dump()
         # v1
         elif hasattr(item, "dict") and callable(item.dict):
-            item = item.dict()
+            result = item.dict()
+            if not result and sys.version_info >= (3, 14):
+                log.warning(
+                    "Pydantic V1 models are not compatible with Python 3.14+. "
+                    "Please upgrade to Pydantic V2. Data may not be serialized correctly."
+                )
+            item = result
     except TypeError as e:
         log.debug(f"Could not serialize Pydantic-like model: {e}")
-        pass
     if isinstance(item, dict):
         return _clean_dict(item)
     if is_dataclass(item) and not isinstance(item, type):