fix: smart union with typeddict (#3543)

pydantic/fields.py

@@ -50,6 +50,7 @@ from .utils import (
     ValueItems,
     get_discriminator_alias_and_values,
     get_unique_discriminator_alias,
+    lenient_isinstance,
     lenient_issubclass,
     sequence_like,
     smart_deepcopy,
@@ -1048,7 +1049,7 @@ class ModelField(Representation):
                             return v, None
                     except TypeError:
                         # compound type
-                        if isinstance(v, get_origin(field.outer_type_)):
+                        if lenient_isinstance(v, get_origin(field.outer_type_)):
                             value, error = field.validate(v, values, loc=loc, cls=cls)
                             if not error:
                                 return value, None

pydantic/utils.py

@@ -53,6 +53,7 @@ __all__ = (
     'import_string',
     'sequence_like',
     'validate_field_name',
+    'lenient_isinstance',
     'lenient_issubclass',
     'in_ipython',
     'deep_update',
@@ -163,6 +164,13 @@ def validate_field_name(bases: List[Type['BaseModel']], field_name: str) -> None
             )
 
 
+def lenient_isinstance(o: Any, class_or_tuple: Union[Type[Any], Tuple[Type[Any], ...]]) -> bool:
+    try:
+        return isinstance(o, class_or_tuple)
+    except TypeError:
+        return False
+
+
 def lenient_issubclass(cls: Any, class_or_tuple: Union[Type[Any], Tuple[Type[Any], ...]]) -> bool:
     try:
         return isinstance(cls, type) and issubclass(cls, class_or_tuple)

tests/test_types.py

@@ -27,7 +27,7 @@ from typing import (
 from uuid import UUID
 
 import pytest
-from typing_extensions import Literal
+from typing_extensions import Literal, TypedDict
 
 from pydantic import (
     UUID1,
@@ -3120,6 +3120,22 @@ def test_smart_union_compouned_types_edge_case():
     assert Model(x=[1, '2']).x == ['1', '2']
 
 
+def test_smart_union_typeddict():
+    class Dict1(TypedDict):
+        foo: str
+
+    class Dict2(TypedDict):
+        bar: str
+
+    class M(BaseModel):
+        d: Union[Dict2, Dict1]
+
+        class Config:
+            smart_union = True
+
+    assert M(d=dict(foo='baz')).d == {'foo': 'baz'}
+
+
 @pytest.mark.parametrize(
     'value,result',
     (