feat: add global config

pydantic/__init__.py

@@ -1,5 +1,5 @@
 # flake8: noqa
-from . import dataclasses
+from . import dataclasses, global_config
 from .class_validators import root_validator, validator
 from .decorator import validate_arguments
 from .env_settings import BaseSettings
@@ -16,6 +16,8 @@
 # WARNING __all__ from .errors is not included here, it will be removed as an export here in v2
 # please use "from pydantic.errors import ..." instead
 __all__ = [
+    # global config
+    'global_config',
     # dataclasses
     'dataclasses',
     # class_validators

pydantic/global_config.py

@@ -0,0 +1 @@
+COPY_ON_MODEL_VALIDATION = True

pydantic/main.py

@@ -662,7 +662,9 @@ def validate(cls: Type['Model'], value: Any) -> 'Model':
         if isinstance(value, dict):
             return cls(**value)
         elif isinstance(value, cls):
-            return value
+            from .global_config import COPY_ON_MODEL_VALIDATION
+
+            return value.copy() if COPY_ON_MODEL_VALIDATION else value
         elif cls.__config__.orm_mode:
             return cls.from_orm(value)
         elif cls.__custom_root_type__:

tests/conftest.py

@@ -85,3 +85,13 @@ def run(source_code_or_function, rewrite_assertions=True):
         return module
 
     return run
+
+
+@pytest.fixture
+def mock_global_config(mocker):
+    def inner(global_config_flag: str, desired_flag_value: bool):
+        import pydantic.global_config as GLOBAL_CONFIG
+
+        mocker.patch.object(GLOBAL_CONFIG, global_config_flag, new=desired_flag_value)
+
+    return inner

tests/test_main.py

@@ -1427,21 +1427,37 @@ class M(BaseModel):
     get_type_hints(M.__config__)
 
 
-def test_inherited_model_field():
+def test_inherited_model_field_default():
+    """By default submodels are copied on validation"""
+
     class Image(BaseModel):
         path: str
 
         def __hash__(self):
             return id(self)
 
     class Item(BaseModel):
-        images: List[Image]
+        image: Image
+
+    image = Image(path='my_image1.png')
+
+    item = Item(image=image)
+    assert item.image is not image
+
+
+def test_inherited_model_field_no_copy(mock_global_config):
+    mock_global_config('COPY_ON_MODEL_VALIDATION', False)
+
+    class Image(BaseModel):
+        path: str
+
+        def __hash__(self):
+            return id(self)
 
-    image_1 = Image(path='my_image1.png')
-    image_2 = Image(path='my_image2.png')
+    class Item(BaseModel):
+        image: Image
 
-    item = Item(images={image_1, image_2})
-    print(image_1 in item.images)
+    image = Image(path='my_image1.png')
 
-    assert id(image_1) == id(item.images[0])
-    assert id(image_2) == id(item.images[1])
+    item = Item(image=image)
+    assert item.image is image