fix: ignore __doc__ as valid private attribute (#2091)

closes #2090

Author: PrettyWood

changes/2090-PrettyWood.md

@@ -0,0 +1 @@
+Ignore `__doc__` as private attribute when `Config.underscore_attrs_are_private` is set

pydantic/utils.py

@@ -631,4 +631,10 @@ def is_valid_field(name: str) -> bool:
 
 
 def is_valid_private_name(name: str) -> bool:
-    return not is_valid_field(name) and name not in {'__annotations__', '__classcell__', '__module__', '__qualname__'}
+    return not is_valid_field(name) and name not in {
+        '__annotations__',
+        '__classcell__',
+        '__doc__',
+        '__module__',
+        '__qualname__',
+    }

tests/test_private_attributes.py

@@ -55,6 +55,8 @@ class Model(BaseModel):
 
 def test_private_attribute_annotation():
     class Model(BaseModel):
+        """The best model"""
+
         __foo__: str
 
         class Config:
@@ -63,6 +65,7 @@ class Config:
     assert Model.__slots__ == {'__foo__'}
     assert repr(Model.__foo__) == "<member '__foo__' of 'Model' objects>"
     assert Model.__private_attributes__ == {'__foo__': PrivateAttr(Undefined)}
+    assert repr(Model.__doc__) == "'The best model'"
 
     m = Model()
     with pytest.raises(AttributeError):