refactor: change pydantic dataclass decorator (#2557)

* refactor: rewrite the whole pydantic dataclass logic

* test: add tests for issue 2162

* test: add tests for issue 2383

* test: add tests for issue 2398

* test: add tests for issue 2424

* test: add tests for issue 2541

* test: add tests for issue 2555

* refactor: polish

* change default and support 3.6

* fix coverage

* fix mypy and text

* typos

* test: add tests for issue 2594

* fix: forward doc for schema description

* add change

* chore: small changes from review

* refactor: avoid extra __pydantic_run_validation__ parameter

* small tweaks

* remove wrapper

* support 3.6

* fix: mypy

* rewrite doc

* add docs

* wrapper is removed now

* a bit more docs

* code review

* faster dict update

* add test for issue 3162

* add test for issue 3011

* feat: add `Config.post_init_after_validation`

* allow config via dict

* fix cython and TypedDict

* chore: typo

* move `compiled` in `version.py`

* refactor: switch from `Config.post_init_after_validation` to \'post_init_call`

* add dataclass isinstance support

* avoid multi paragraphs in change file

* feat: support `Config.extra`

* refactor: simplify a bit code

* refactor: avoid creating useless functions

* refactor: simplify `is_builtin_dataclass`

* support extra in post_init

* docs: add warning on config extra

* fix #3713 compatibility

* update docs

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

changes/2557-PrettyWood.md

@@ -0,0 +1,9 @@
+Refactor the whole _pydantic_ `dataclass` decorator to really act like its standard lib equivalent.
+It hence keeps `__eq__`, `__hash__`, ... and makes comparison with its non-validated version possible.
+It also fixes usage of `frozen` dataclasses in fields and usage of `default_factory` in nested dataclasses.
+The support of `Config.extra` has been added.
+Finally, config customization directly via a `dict` is now possible.
+<br/><br/>
+**BREAKING CHANGES**
+- The `compiled` boolean (whether _pydantic_ is compiled with cython) has been moved from `main.py` to `version.py`
+- Now that `Config.extra` is supported, `dataclass` ignores by default extra arguments (like `BaseModel`)

docs/examples/dataclasses_config.py

@@ -0,0 +1,26 @@
+from pydantic import ConfigDict
+from pydantic.dataclasses import dataclass
+
+
+# Option 1 - use directly a dict
+# Note: `mypy` will still raise typo error
+@dataclass(config=dict(validate_assignment=True))
+class MyDataclass1:
+    a: int
+
+
+# Option 2 - use `ConfigDict`
+# (same as before at runtime since it's a `TypedDict` but with intellisense)
+@dataclass(config=ConfigDict(validate_assignment=True))
+class MyDataclass2:
+    a: int
+
+
+# Option 3 - use a `Config` class like for a `BaseModel`
+class Config:
+    validate_assignment = True
+
+
+@dataclass(config=Config)
+class MyDataclass3:
+    a: int

docs/examples/dataclasses_stdlib_run_validation.py

@@ -0,0 +1,30 @@
+import dataclasses
+
+from pydantic import ValidationError
+from pydantic.dataclasses import dataclass as pydantic_dataclass, set_validation
+
+
+@dataclasses.dataclass
+class User:
+    id: int
+    name: str
+
+
+# Enhance stdlib dataclass
+pydantic_dataclass(User)
+
+
+user1 = User(id='whatever', name='I want')
+
+# validate data of `user1`
+try:
+    user1.__pydantic_validate_values__()
+except ValidationError as e:
+    print(e)
+
+# Enforce validation
+try:
+    with set_validation(User, True):
+        User(id='whatever', name='I want')
+except ValidationError as e:
+    print(e)

docs/examples/dataclasses_stdlib_to_pydantic.py

@@ -16,20 +16,32 @@ class File(Meta):
     filename: str
 
 
-File = pydantic.dataclasses.dataclass(File)
+# `ValidatedFile` will be a proxy around `File`
+ValidatedFile = pydantic.dataclasses.dataclass(File)
 
-file = File(
+# the original dataclass is the `__dataclass__` attribute
+assert ValidatedFile.__dataclass__ is File
+
+
+validated_file = ValidatedFile(
     filename=b'thefilename',
     modified_date='2020-01-01T00:00',
     seen_count='7',
 )
-print(file)
+print(validated_file)
 
 try:
-    File(
+    ValidatedFile(
         filename=['not', 'a', 'string'],
         modified_date=None,
         seen_count=3,
     )
 except pydantic.ValidationError as e:
     print(e)
+
+# `File` is not altered and still does no validation by default
+print(File(
+    filename=['not', 'a', 'string'],
+    modified_date=None,
+    seen_count=3,
+))

docs/usage/dataclasses.md

@@ -18,7 +18,7 @@ You can use all the standard _pydantic_ field types, and the resulting dataclass
 created by the standard library `dataclass` decorator.
 
 The underlying model and its schema can be accessed through `__pydantic_model__`.
-Also, fields that require a `default_factory` can be specified by a `dataclasses.field`.
+Also, fields that require a `default_factory` can be specified by either a `pydantic.Field` or a `dataclasses.field`.
 
 ```py
 {!.tmp_examples/dataclasses_default_schema.py!}
@@ -34,6 +34,20 @@ keyword argument `config` which has the same meaning as [Config](model_config.md
 For more information about combining validators with dataclasses, see
 [dataclass validators](validators.md#dataclass-validators).
 
+## Dataclass Config
+
+If you want to modify the `Config` like you would with a `BaseModel`, you have three options:
+
+```py
+{!.tmp_examples/dataclasses_config.py!}
+```
+
+!!! warning
+    After v1.10, _pydantic_ dataclasses support `Config.extra` but some default behaviour of stdlib dataclasses
+    may prevail. For example, when `print`ing a _pydantic_ dataclass with allowed extra fields, it will still
+    use the `__str__` method of stdlib dataclass and show only the required fields.
+    This may be improved further in the future.
+
 ## Nested dataclasses
 
 Nested dataclasses are supported both in dataclasses and normal models.
@@ -51,12 +65,25 @@ Dataclasses attributes can be populated by tuples, dictionaries or instances of
 
 Stdlib dataclasses (nested or not) can be easily converted into _pydantic_ dataclasses by just decorating
 them with `pydantic.dataclasses.dataclass`.
+_Pydantic_ will enhance the given stdlib dataclass but won't alter the default behaviour (i.e. without validation).
+It will instead create a wrapper around it to trigger validation that will act like a plain proxy.
+The stdlib dataclass can still be accessed via the `__dataclass__` attribute (see example below).
 
 ```py
 {!.tmp_examples/dataclasses_stdlib_to_pydantic.py!}
 ```
 _(This script is complete, it should run "as is")_
 
+### Choose when to trigger validation
+
+As soon as your stdlib dataclass has been decorated with _pydantic_ dataclass decorator, magic methods have been
+added to validate input data. If you want, you can still keep using your dataclass and choose when to trigger it.
+
+```py
+{!.tmp_examples/dataclasses_stdlib_run_validation.py!}
+```
+_(This script is complete, it should run "as is")_
+
 ### Inherit from stdlib dataclasses
 
 Stdlib dataclasses (nested or not) can also be inherited and _pydantic_ will automatically validate
@@ -95,6 +122,11 @@ When you initialize a dataclass, it is possible to execute code *after* validati
 with the help of `__post_init_post_parse__`. This is not the same as `__post_init__`, which executes
 code *before* validation.
 
+!!! tip
+    If you use a stdlib `dataclass`, you may only have `__post_init__` available and wish the validation to
+    be done before. In this case you can set `Config.post_init_call = 'after_validation'`
+
+
 ```py
 {!.tmp_examples/dataclasses_post_init_post_parse.py!}
 ```

docs/usage/model_config.md

@@ -118,6 +118,10 @@ not be included in the model schemas. **Note**: this means that attributes on th
 **`smart_union`**
 : whether _pydantic_ should try to check all types inside `Union` to prevent undesired coercion; see [the dedicated section](#smart-union)
 
+**`post_init_call`**
+: whether stdlib dataclasses `__post_init__` should be run before (default behaviour with value `'before_validation'`)
+  or after (value `'after_validation'`) parsing and validation when they are [converted](dataclasses.md#stdlib-dataclasses-and-_pydantic_-dataclasses).
+
 ## Change behaviour globally
 
 If you wish to change the behaviour of _pydantic_ globally, you can create your own custom `BaseModel`

pydantic/__init__.py

@@ -2,7 +2,7 @@
 from . import dataclasses
 from .annotated_types import create_model_from_namedtuple, create_model_from_typeddict
 from .class_validators import root_validator, validator
-from .config import BaseConfig, Extra
+from .config import BaseConfig, ConfigDict, Extra
 from .decorator import validate_arguments
 from .env_settings import BaseSettings
 from .error_wrappers import ValidationError
@@ -13,7 +13,7 @@
 from .parse import Protocol
 from .tools import *
 from .types import *
-from .version import VERSION
+from .version import VERSION, compiled
 
 __version__ = VERSION
 
@@ -30,6 +30,7 @@
     'validator',
     # config
     'BaseConfig',
+    'ConfigDict',
     'Extra',
     # decorator
     'validate_arguments',
@@ -42,7 +43,6 @@
     'Required',
     # main
     'BaseModel',
-    'compiled',
     'create_model',
     'validate_model',
     # network
@@ -120,5 +120,6 @@
     'PastDate',
     'FutureDate',
     # version
+    'compiled',
     'VERSION',
 ]

pydantic/config.py

@@ -4,6 +4,7 @@
 
 from .typing import AnyCallable
 from .utils import GetterDict
+from .version import compiled
 
 if TYPE_CHECKING:
     from typing import overload
@@ -27,7 +28,7 @@ def __call__(self, schema: Dict[str, Any], model_class: Type[BaseModel]) -> None
 else:
     SchemaExtraCallable = Callable[..., None]
 
-__all__ = 'BaseConfig', 'Extra', 'inherit_config', 'prepare_config'
+__all__ = 'BaseConfig', 'ConfigDict', 'get_config', 'Extra', 'inherit_config', 'prepare_config'
 
 
 class Extra(str, Enum):
@@ -36,6 +37,46 @@ class Extra(str, Enum):
     forbid = 'forbid'
 
 
+# https://github.com/cython/cython/issues/4003
+# Will be fixed with Cython 3 but still in alpha right now
+if not compiled:
+    from typing_extensions import Literal, TypedDict
+
+    class ConfigDict(TypedDict, total=False):
+        title: Optional[str]
+        anystr_lower: bool
+        anystr_strip_whitespace: bool
+        min_anystr_length: int
+        max_anystr_length: Optional[int]
+        validate_all: bool
+        extra: Extra
+        allow_mutation: bool
+        frozen: bool
+        allow_population_by_field_name: bool
+        use_enum_values: bool
+        fields: Dict[str, Union[str, Dict[str, str]]]
+        validate_assignment: bool
+        error_msg_templates: Dict[str, str]
+        arbitrary_types_allowed: bool
+        orm_mode: bool
+        getter_dict: Type[GetterDict]
+        alias_generator: Optional[Callable[[str], str]]
+        keep_untouched: Tuple[type, ...]
+        schema_extra: Union[Dict[str, Any], 'SchemaExtraCallable']
+        json_loads: Callable[[str], Any]
+        json_dumps: Callable[..., str]
+        json_encoders: Dict[Type[Any], AnyCallable]
+        underscore_attrs_are_private: bool
+
+        # whether or not inherited models as fields should be reconstructed as base model
+        copy_on_model_validation: bool
+        # whether dataclass `__post_init__` should be run after validation
+        post_init_call: Literal['before_validation', 'after_validation']
+
+else:
+    ConfigDict = dict  # type: ignore
+
+
 class BaseConfig:
     title: Optional[str] = None
     anystr_lower: bool = False
@@ -66,6 +107,8 @@ class BaseConfig:
     copy_on_model_validation: bool = True
     # whether `Union` should check all allowed types before even trying to coerce
     smart_union: bool = False
+    # whether dataclass `__post_init__` should be run before or after validation
+    post_init_call: Literal['before_validation', 'after_validation'] = 'before_validation'
 
     @classmethod
     def get_field_info(cls, name: str) -> Dict[str, Any]:
@@ -100,6 +143,25 @@ def prepare_field(cls, field: 'ModelField') -> None:
         pass
 
 
+def get_config(config: Union[ConfigDict, Type[BaseConfig], None]) -> Type[BaseConfig]:
+    if config is None:
+        return BaseConfig
+
+    else:
+        config_dict = (
+            config
+            if isinstance(config, dict)
+            else {k: getattr(config, k) for k in dir(config) if not k.startswith('__')}
+        )
+
+        class Config(BaseConfig):
+            ...
+
+        for k, v in config_dict.items():
+            setattr(Config, k, v)
+        return Config
+
+
 def inherit_config(self_config: 'ConfigType', parent_config: 'ConfigType', **namespace: Any) -> 'ConfigType':
     if not self_config:
         base_classes: Tuple['ConfigType', ...] = (parent_config,)