From ce67660d2fa3003807718bdcb5459cfae97e6d82 Mon Sep 17 00:00:00 2001
From: Arseny Boykov <36469655+MrMrRobat@users.noreply.github.com>
Date: Mon, 22 Feb 2021 20:10:04 +0300
Subject: [PATCH] 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                  |  1 +
 docs/examples/model_config_class_kwargs.py | 11 ++++++++
 docs/usage/model_config.md                 |  7 +++++-
 pydantic/main.py                           | 23 ++++++++++-------
 tests/test_main.py                         | 29 ++++++++++++++++++++++
 5 files changed, 61 insertions(+), 10 deletions(-)
 create mode 100644 changes/2356-MrMrRobat.md
 create mode 100644 docs/examples/model_config_class_kwargs.py

diff --git a/changes/2356-MrMrRobat.md b/changes/2356-MrMrRobat.md
new file mode 100644
index 0000000000..d4adb3c2be
--- /dev/null
+++ b/changes/2356-MrMrRobat.md
@@ -0,0 +1 @@
+Allow configuring models through class kwargs
\ No newline at end of file
diff --git a/docs/examples/model_config_class_kwargs.py b/docs/examples/model_config_class_kwargs.py
new file mode 100644
index 0000000000..3a1841c57b
--- /dev/null
+++ b/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)
diff --git a/docs/usage/model_config.md b/docs/usage/model_config.md
index 91c8d3d649..c2c09fc930 100644
--- a/docs/usage/model_config.md
+++ b/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!}
 ```
diff --git a/pydantic/main.py b/pydantic/main.py
index 0f833f16fa..fccdff6685 100644
--- a/pydantic/main.py
+++ b/pydantic/main.py
@@ -168,18 +168,18 @@ def prepare_field(cls, field: 'ModelField') -> None:
         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 @@ def __new__(mcs, name, bases, namespace, **kwargs):  # noqa C901
                 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)
 
diff --git a/tests/test_main.py b/tests/test_main.py
index c6109f8427..2094734097 100644
--- a/tests/test_main.py
+++ b/tests/test_main.py
@@ -1550,3 +1550,32 @@ class Item(BaseModel):
 
     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'