streamlit · lukasmasuch · Dec 22, 2025 · Dec 14, 2025 · Dec 14, 2025 · Dec 14, 2025
diff --git a/lib/streamlit/dataframe_util.py b/lib/streamlit/dataframe_util.py
@@ -41,12 +41,14 @@
 from streamlit import config, errors, logger, string_util
 from streamlit.type_util import (
     CustomDict,
+    dump_pydantic_sequence,
     has_callable_attr,
     is_custom_dict,
     is_dataclass_instance,
     is_list_like,
     is_namedtuple,
     is_pydantic_model,
+    is_sequence_of_pydantic_models,
     is_type,
     is_version_less_than,
 )
@@ -703,6 +705,14 @@ def convert_anything_to_pandas_df(
     if is_snowpark_row_list(data):
         return pd.DataFrame([row.as_dict() for row in data])
 
+    if is_sequence_of_pydantic_models(data):
+        # Try to convert pydantic models to DataFrame. If some elements are not
+        # pydantic models (mixed sequence), fall through to pandas' native handling.
+        try:
+            return pd.DataFrame(dump_pydantic_sequence(data))
+        except AttributeError:
+            pass
+
     if has_callable_attr(data, "to_pandas"):
         return pd.DataFrame(data.to_pandas())
 
@@ -1242,7 +1252,7 @@ def determine_data_format(input_data: Any) -> DataFormat:
         # This should always contain at least one element,
         # otherwise the values type from infer_dtype would have been empty
         first_element = next(iter(input_data))
-        if isinstance(first_element, dict):
+        if isinstance(first_element, dict) or is_pydantic_model(first_element):
             return DataFormat.LIST_OF_RECORDS
         if isinstance(first_element, (list, tuple, set, frozenset)):
             return DataFormat.LIST_OF_ROWS

diff --git a/lib/streamlit/elements/json.py b/lib/streamlit/elements/json.py
@@ -27,10 +27,12 @@
 from streamlit.proto.Json_pb2 import Json as JsonProto
 from streamlit.runtime.metrics_util import gather_metrics
 from streamlit.type_util import (
+    dump_pydantic_sequence,
     is_custom_dict,
     is_list_like,
     is_namedtuple,
     is_pydantic_model,
+    is_sequence_of_pydantic_models,
 )
 
 if TYPE_CHECKING:
@@ -120,7 +122,14 @@ def json(
             body = dict(body)  # type: ignore
 
         if is_list_like(body):
-            body = list(body)  # ty: ignore[invalid-argument-type]
+            if is_sequence_of_pydantic_models(body):
+                try:
+                    body = dump_pydantic_sequence(body)
+                except AttributeError:
+                    # Fallback to list(body) if it contains non-Pydantic models:
+                    body = list(body)  # ty: ignore[invalid-argument-type]
+            else:
+                body = list(body)  # ty: ignore[invalid-argument-type]
 
         if not isinstance(body, str):
             try:

diff --git a/lib/streamlit/type_util.py b/lib/streamlit/type_util.py
@@ -331,6 +331,24 @@ def is_pydantic_model(obj: object) -> bool:
     return _is_type_instance(obj, "pydantic.main.BaseModel")
 
 
+def is_sequence_of_pydantic_models(obj: object) -> TypeGuard[Sequence[Any]]:
+    """True if obj is a non-empty list/tuple/set/frozenset of Pydantic model instances."""
+    if not isinstance(obj, (list, tuple, set, frozenset)) or len(obj) == 0:
+        return False
+    first_element = next(iter(obj))
+    return is_pydantic_model(first_element)
+
+
+def dump_pydantic_sequence(obj: Sequence[object]) -> list[dict[str, Any]]:
+    """Dump a sequence of Pydantic models to a list of dictionaries."""
+    first_element = next(iter(obj))
+    # Pydantic v2 uses model_dump(), v1 uses dict()
+    if has_callable_attr(first_element, "model_dump"):
+        # Use mode="json" to ensure proper serialization of types like Decimal
+        return [item.model_dump(mode="json") for item in obj]  # type: ignore
+    return [item.dict() for item in obj]  # type: ignore
+
+
 def _is_from_streamlit(obj: object) -> bool:
     """True if the object is from the streamlit package."""
     return obj.__class__.__module__.startswith("streamlit")

diff --git a/lib/tests/streamlit/data_test_cases.py b/lib/tests/streamlit/data_test_cases.py
@@ -1250,6 +1250,61 @@ class ElementPydanticModel(BaseModel):
                     dict,
                 ),
             ),
+            (
+                "List of Pydantic Models",
+                [
+                    ElementPydanticModel(
+                        name="st.number_input", is_widget=True, usage=0.32
+                    ),
+                    ElementPydanticModel(
+                        name="st.text_input", is_widget=True, usage=0.45
+                    ),
+                ],
+                CaseMetadata(
+                    2,
+                    3,
+                    DataFormat.LIST_OF_RECORDS,
+                    [
+                        ElementPydanticModel(
+                            name="st.number_input", is_widget=True, usage=0.32
+                        ),
+                        ElementPydanticModel(
+                            name="st.text_input", is_widget=True, usage=0.45
+                        ),
+                    ],
+                    "json",
+                    False,
+                    list,
+                ),
+            ),
+            (
+                "Tuple of Pydantic Models",
+                (
+                    ElementPydanticModel(
+                        name="st.number_input", is_widget=True, usage=0.32
+                    ),
+                    ElementPydanticModel(
+                        name="st.text_input", is_widget=True, usage=0.45
+                    ),
+                ),
+                CaseMetadata(
+                    2,
+                    3,
+                    DataFormat.LIST_OF_RECORDS,
+                    [
+                        ElementPydanticModel(
+                            name="st.number_input", is_widget=True, usage=0.32
+                        ),
+                        ElementPydanticModel(
+                            name="st.text_input", is_widget=True, usage=0.45
+                        ),
+                    ],
+                    "json",
+                    False,
+                    # LIST_OF_RECORDS always converts back to list, not tuple
+                    list,
+                ),
+            ),
         ]
     )
 except ModuleNotFoundError: