Allow to configure models through class kwargs (#2356)

* add support for class kwargs config

* reformat tests

* add changes file and docs

* fix linting in 'inherit_config'

* tweak docs

Co-authored-by: Samuel Colvin <s@muelcolvin.com>

changes/2356-MrMrRobat.md

@@ -0,0 +1 @@
+Allow configuring models through class kwargs

docs/examples/model_config_class_kwargs.py

@@ -0,0 +1,11 @@
+from pydantic import BaseModel, ValidationError, Extra
+
+
+class Model(BaseModel, extra=Extra.forbid):
+    a: str
+
+
+try:
+    Model(a='spam', b='oh no')
+except ValidationError as e:
+    print(e)

docs/usage/model_config.md

@@ -89,8 +89,13 @@ not be included in the model schemas. **Note**: this means that attributes on th
 ```
 _(This script is complete, it should run "as is")_
 
-Similarly, if using the `@dataclass` decorator:
+Also, you can specify config options as model class kwargs:
+```py
+{!.tmp_examples/model_config_class_kwargs.py!}
+```
+_(This script is complete, it should run "as is")_
 
+Similarly, if using the `@dataclass` decorator:
 ```py
 {!.tmp_examples/model_config_dataclass.py!}
 ```

pydantic/main.py

@@ -168,18 +168,18 @@ class BaseConfig:
         pass
 
 
-def inherit_config(self_config: 'ConfigType', parent_config: 'ConfigType') -> 'ConfigType':
-    namespace = {}
+def inherit_config(self_config: 'ConfigType', parent_config: 'ConfigType', **namespace: Any) -> 'ConfigType':
     if not self_config:
-        base_classes = (parent_config,)
+        base_classes: Tuple['ConfigType', ...] = (parent_config,)
     elif self_config == parent_config:
         base_classes = (self_config,)
     else:
-        base_classes = self_config, parent_config  # type: ignore
-        namespace['json_encoders'] = {
-            **getattr(parent_config, 'json_encoders', {}),
-            **getattr(self_config, 'json_encoders', {}),
-        }
+        base_classes = self_config, parent_config
+
+    namespace['json_encoders'] = {
+        **getattr(parent_config, 'json_encoders', {}),
+        **getattr(self_config, 'json_encoders', {}),
+    }
 
     return type('Config', base_classes, namespace)
 
@@ -251,7 +251,12 @@ class ModelMetaclass(ABCMeta):
                 private_attributes.update(base.__private_attributes__)
                 class_vars.update(base.__class_vars__)
 
-        config = inherit_config(namespace.get('Config'), config)
+        config_kwargs = {key: kwargs.pop(key) for key in kwargs.keys() & BaseConfig.__dict__.keys()}
+        config_from_namespace = namespace.get('Config')
+        if config_kwargs and config_from_namespace:
+            raise TypeError('Specifying config in two places is ambiguous, use either Config attribute or class kwargs')
+        config = inherit_config(config_from_namespace, config, **config_kwargs)
+
         validators = inherit_validators(extract_validators(namespace), validators)
         vg = ValidatorGroup(validators)
 

tests/test_main.py

@@ -1550,3 +1550,32 @@ def test_inherited_model_field_untouched():
 
     assert id(image_1) == id(item.images[0])
     assert id(image_2) == id(item.images[1])
+
+
+def test_class_kwargs_config():
+    class Base(BaseModel, extra='forbid', alias_generator=str.upper):
+        a: int
+
+    assert Base.__config__.extra is Extra.forbid
+    assert Base.__config__.alias_generator is str.upper
+    assert Base.__fields__['a'].alias == 'A'
+
+    class Model(Base, extra='allow'):
+        b: int
+
+    assert Model.__config__.extra is Extra.allow  # overwritten as intended
+    assert Model.__config__.alias_generator is str.upper  # inherited as intended
+    assert Model.__fields__['b'].alias == 'B'  # alias_generator still works
+
+
+def test_class_kwargs_config_and_attr_conflict():
+
+    with pytest.raises(
+        TypeError, match='Specifying config in two places is ambiguous, use either Config attribute or class kwargs'
+    ):
+
+        class Model(BaseModel, extra='allow'):
+            b: int
+
+            class Config:
+                extra = 'forbid'