Re-allow nested inherited inits without breaking self attribute

This commit enables nested model `__init__` statements to be executed
while still allowing `self` as an argument.

Effectively reverses the changes from pydantic#632 while still enabling the
feature it implemented. In theory, there will still be a collision if
someone ever tried to use `pydantic_base_model/settings_init` as an arg,
but I don't know how to engineer a case where a collision would *never*
happen, I'm not sure there is one.

This commit also added a test for both BaseModel` and `BaseSettings` for
both the `self`-as-a-parameter and the nested `__init__` features since
`BaseSettings` now has the same issue as `BaseModel` since it invoked
an `__init__` with self.

I have added a comment under the `__init__` for both `BaseModel` and
`BaseSetting` since not having `self` as the first arg is such a
rarity within Python that it will likely confuse future developers who
encounter it.

The actual name of the variable referencing the class itself can be
up for debate.

pydantic/env_settings.py

@@ -20,8 +20,9 @@ class BaseSettings(BaseModel):
     Heroku and any 12 factor app design.
     """
 
-    def __init__(self, **values: Any) -> None:
-        super().__init__(**self._build_values(values))
+    def __init__(pydantic_base_settings_init, **values: Any) -> None:
+        # Uses something other than `self` the first arg to allow "self" as a settable attribute
+        super().__init__(**pydantic_base_settings_init._build_values(values))
 
     def _build_values(self, init_kwargs: Dict[str, Any]) -> Dict[str, Any]:
         return {**self._build_environ(), **init_kwargs}

pydantic/main.py

@@ -263,13 +263,14 @@ class BaseModel(metaclass=MetaModel):
     Config = BaseConfig
     __slots__ = ('__values__', '__fields_set__')
 
-    def __init__(self, **data: Any) -> None:
+    def __init__(pydantic_base_model_init, **data: Any) -> None:
+        # Uses something other than `self` the first arg to allow "self" as a settable attribute
         if TYPE_CHECKING:  # pragma: no cover
-            self.__values__: Dict[str, Any] = {}
-            self.__fields_set__: 'SetStr' = set()
-        values, fields_set, _ = validate_model(self, data)
-        object.__setattr__(self, '__values__', values)
-        object.__setattr__(self, '__fields_set__', fields_set)
+            pydantic_base_model_init.__values__: Dict[str, Any] = {}
+            pydantic_base_model_init.__fields_set__: 'SetStr' = set()
+        values, fields_set, _ = validate_model(pydantic_base_model_init, data)
+        object.__setattr__(pydantic_base_model_init, '__values__', values)
+        object.__setattr__(pydantic_base_model_init, '__fields_set__', fields_set)
 
     @no_type_check
     def __getattr__(self, name):
@@ -358,12 +359,7 @@ def parse_obj(cls: Type['Model'], obj: Any) -> 'Model':
                 except (TypeError, ValueError) as e:
                     exc = TypeError(f'{cls.__name__} expected dict not {type(obj).__name__}')
                     raise ValidationError([ErrorWrapper(exc, loc='__obj__')]) from e
-
-        m = cls.__new__(cls)
-        values, fields_set, _ = validate_model(m, obj)
-        object.__setattr__(m, '__values__', values)
-        object.__setattr__(m, '__fields_set__', fields_set)
-        return m
+        return cls(**obj)
 
     @classmethod
     def parse_raw(
@@ -477,14 +473,14 @@ def __get_validators__(cls) -> 'CallableGenerator':
     @classmethod
     def validate(cls: Type['Model'], value: Any) -> 'Model':
         if isinstance(value, dict):
-            return cls.parse_obj(value)
+            return cls(**value)
         elif isinstance(value, cls):
             return value.copy()
         elif cls.__config__.orm_mode:
             return cls.from_orm(value)
         else:
             with change_exception(DictError, TypeError, ValueError):
-                return cls.parse_obj(value)
+                return cls(**dict(value))
 
     @classmethod
     def _decompose_class(cls: Type['Model'], obj: Any) -> GetterDict:

tests/test_edge_cases.py

@@ -8,6 +8,7 @@
 from pydantic import (
     BaseConfig,
     BaseModel,
+    BaseSettings,
     Extra,
     NoneStrBytes,
     StrBytes,
@@ -897,12 +898,35 @@ class Model(BaseModel):
     }
 
 
-def test_self_recursive():
-    class SubModel(BaseModel):
+@pytest.mark.parametrize('model', [BaseModel, BaseSettings])
+def test_self_recursive(model):
+    class SubModel(model):
         self: int
 
-    class Model(BaseModel):
+    class Model(model):
         sm: SubModel
 
     m = Model.parse_obj({'sm': {'self': '123'}})
     assert m.dict() == {'sm': {'self': 123}}
+
+
+@pytest.mark.parametrize('model', [BaseModel, BaseSettings])
+def test_nested_init(model):
+    class NestedModel(model):
+        self: str
+        modified_number: int = 1
+
+        def __init__(someinit, **kwargs):
+            super().__init__(**kwargs)
+            someinit.modified_number += 1
+
+    class TopModel(model):
+        self: str
+        nest: NestedModel
+
+    m = TopModel.parse_obj(dict(self="Top Model",
+                                nest=dict(self="Nested Model",
+                                          modified_number=0)))
+    assert m.self == "Top Model"
+    assert m.nest.self == "Nested Model"
+    assert m.nest.modified_number == 1