Address case where model_construct on a class which defines model_pos…

…t_init fails with AttributeError: __pydantic_private__ when subsequently model_copy'd (#9168)

Co-authored-by: David Grimes <david.grimes@axial.net>

pydantic/main.py

@@ -742,7 +742,7 @@ def __copy__(self: Model) -> Model:
         _object_setattr(m, '__pydantic_extra__', copy(self.__pydantic_extra__))
         _object_setattr(m, '__pydantic_fields_set__', copy(self.__pydantic_fields_set__))
 
-        if self.__pydantic_private__ is None:
+        if not hasattr(self, '__pydantic_private__') or self.__pydantic_private__ is None:
             _object_setattr(m, '__pydantic_private__', None)
         else:
             _object_setattr(
@@ -763,7 +763,7 @@ def __deepcopy__(self: Model, memo: dict[int, Any] | None = None) -> Model:
         # and attempting a deepcopy would be marginally slower.
         _object_setattr(m, '__pydantic_fields_set__', copy(self.__pydantic_fields_set__))
 
-        if self.__pydantic_private__ is None:
+        if not hasattr(self, '__pydantic_private__') or self.__pydantic_private__ is None:
             _object_setattr(m, '__pydantic_private__', None)
         else:
             _object_setattr(
@@ -923,7 +923,7 @@ def __eq__(self, other: Any) -> bool:
                 # Perform common checks first
                 if not (
                     self_type == other_type
-                    and self.__pydantic_private__ == other.__pydantic_private__
+                    and getattr(self, '__pydantic_private__', None) == getattr(other, '__pydantic_private__', None)
                     and self.__pydantic_extra__ == other.__pydantic_extra__
                 ):
                     return False

tests/test_main.py

@@ -3280,3 +3280,17 @@ class Y(BaseModel):
         x: Union[X, None]
 
     assert Y(x={'y': None}).x.y is None
+
+
+def test_model_construct_with_model_post_init_and_model_copy() -> None:
+    class Model(BaseModel):
+        id: int
+
+        def model_post_init(self, context: Any) -> None:
+            super().model_post_init(context)
+
+    m = Model.model_construct(id=1)
+    copy = m.model_copy(deep=True)
+
+    assert m == copy
+    assert id(m) != id(copy)