Support Message.from_dict() as a class and an instance method (#476)

* Make Message.from_dict() a class method

Signed-off-by: Marek Pikuła <marek.pikula@embevity.com>

* Sync 1/2 of review comments

* Sync other half

* Update .pre-commit-config.yaml

* Update __init__.py

* Update utils.py

* Update src/betterproto/__init__.py

* Update .pre-commit-config.yaml

* Update __init__.py

* Update utils.py

* Fix CI again

* Fix failing formatting

---------

Signed-off-by: Marek Pikuła <marek.pikula@embevity.com>
Co-authored-by: James Hilton-Balfe <gobot1234yt@gmail.com>

src/betterproto/__init__.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import dataclasses
 import enum as builtin_enum
 import json
@@ -22,8 +24,8 @@ from itertools import count
 from typing import (
     TYPE_CHECKING,
     Any,
-    BinaryIO,
     Callable,
+    ClassVar,
     Dict,
     Generator,
     Iterable,
@@ -37,6 +39,7 @@ from typing import (
 )
 
 from dateutil.parser import isoparse
+from typing_extensions import Self
 
 from ._types import T
 from ._version import __version__
@@ -47,6 +50,10 @@ from .casing import (
 )
 from .enum import Enum as Enum
 from .grpc.grpclib_client import ServiceStub as ServiceStub
+from .utils import (
+    classproperty,
+    hybridmethod,
+)
 
 
 if TYPE_CHECKING:
@@ -729,6 +736,7 @@ class Message(ABC):
     _serialized_on_wire: bool
     _unknown_fields: bytes
     _group_current: Dict[str, str]
+    _betterproto_meta: ClassVar[ProtoClassMetadata]
 
     def __post_init__(self) -> None:
         # Keep track of whether every field was default
@@ -882,18 +890,18 @@ class Message(ABC):
                 kwargs[name] = value
         return self.__class__(**kwargs)  # type: ignore
 
-    @property
-    def _betterproto(self) -> ProtoClassMetadata:
+    @classproperty
+    def _betterproto(cls: type[Self]) -> ProtoClassMetadata:  # type: ignore
         """
         Lazy initialize metadata for each protobuf class.
         It may be initialized multiple times in a multi-threaded environment,
         but that won't affect the correctness.
         """
-        meta = getattr(self.__class__, "_betterproto_meta", None)
-        if not meta:
-            meta = ProtoClassMetadata(self.__class__)
-            self.__class__._betterproto_meta = meta  # type: ignore
-        return meta
+        try:
+            return cls._betterproto_meta
+        except AttributeError:
+            cls._betterproto_meta = meta = ProtoClassMetadata(cls)
+            return meta
 
     def dump(self, stream: "SupportsWrite[bytes]", delimit: bool = False) -> None:
         """
@@ -1512,7 +1520,91 @@ class Message(ABC):
                     output[cased_name] = value
         return output
 
-    def from_dict(self: T, value: Mapping[str, Any]) -> T:
+    @classmethod
+    def _from_dict_init(cls, mapping: Mapping[str, Any]) -> Mapping[str, Any]:
+        init_kwargs: Dict[str, Any] = {}
+        for key, value in mapping.items():
+            field_name = safe_snake_case(key)
+            try:
+                meta = cls._betterproto.meta_by_field_name[field_name]
+            except KeyError:
+                continue
+            if value is None:
+                continue
+
+            if meta.proto_type == TYPE_MESSAGE:
+                sub_cls = cls._betterproto.cls_by_field[field_name]
+                if sub_cls == datetime:
+                    value = (
+                        [isoparse(item) for item in value]
+                        if isinstance(value, list)
+                        else isoparse(value)
+                    )
+                elif sub_cls == timedelta:
+                    value = (
+                        [timedelta(seconds=float(item[:-1])) for item in value]
+                        if isinstance(value, list)
+                        else timedelta(seconds=float(value[:-1]))
+                    )
+                elif not meta.wraps:
+                    value = (
+                        [sub_cls.from_dict(item) for item in value]
+                        if isinstance(value, list)
+                        else sub_cls.from_dict(value)
+                    )
+            elif meta.map_types and meta.map_types[1] == TYPE_MESSAGE:
+                sub_cls = cls._betterproto.cls_by_field[f"{field_name}.value"]
+                value = {k: sub_cls.from_dict(v) for k, v in value.items()}
+            else:
+                if meta.proto_type in INT_64_TYPES:
+                    value = (
+                        [int(n) for n in value]
+                        if isinstance(value, list)
+                        else int(value)
+                    )
+                elif meta.proto_type == TYPE_BYTES:
+                    value = (
+                        [b64decode(n) for n in value]
+                        if isinstance(value, list)
+                        else b64decode(value)
+                    )
+                elif meta.proto_type == TYPE_ENUM:
+                    enum_cls = cls._betterproto.cls_by_field[field_name]
+                    if isinstance(value, list):
+                        value = [enum_cls.from_string(e) for e in value]
+                    elif isinstance(value, str):
+                        value = enum_cls.from_string(value)
+                elif meta.proto_type in (TYPE_FLOAT, TYPE_DOUBLE):
+                    value = (
+                        [_parse_float(n) for n in value]
+                        if isinstance(value, list)
+                        else _parse_float(value)
+                    )
+
+            init_kwargs[field_name] = value
+        return init_kwargs
+
+    @hybridmethod
+    def from_dict(cls: type[Self], value: Mapping[str, Any]) -> Self:  # type: ignore
+        """
+        Parse the key/value pairs into the a new message instance.
+
+        Parameters
+        -----------
+        value: Dict[:class:`str`, Any]
+            The dictionary to parse from.
+
+        Returns
+        --------
+        :class:`Message`
+            The initialized message.
+        """
+        self = cls(**cls._from_dict_init(value))
+        self._serialized_on_wire = True
+        return self
+
+    @from_dict.instancemethod
+    def from_dict(self, value: Mapping[str, Any]) -> Self:
         """
         Parse the key/value pairs into the current message instance. This returns the
         instance itself and is therefore assignable and chainable.
@@ -1528,71 +1620,8 @@ class Message(ABC):
             The initialized message.
         """
         self._serialized_on_wire = True
-        for key in value:
-            field_name = safe_snake_case(key)
-            meta = self._betterproto.meta_by_field_name.get(field_name)
-            if not meta:
-                continue
-
-            if value[key] is not None:
-                if meta.proto_type == TYPE_MESSAGE:
-                    v = self._get_field_default(field_name)
-                    cls = self._betterproto.cls_by_field[field_name]
-                    if isinstance(v, list):
-                        if cls == datetime:
-                            v = [isoparse(item) for item in value[key]]
-                        elif cls == timedelta:
-                            v = [
-                                timedelta(seconds=float(item[:-1]))
-                                for item in value[key]
-                            ]
-                        else:
-                            v = [cls().from_dict(item) for item in value[key]]
-                    elif cls == datetime:
-                        v = isoparse(value[key])
-                        setattr(self, field_name, v)
-                    elif cls == timedelta:
-                        v = timedelta(seconds=float(value[key][:-1]))
-                        setattr(self, field_name, v)
-                    elif meta.wraps:
-                        setattr(self, field_name, value[key])
-                    elif v is None:
-                        setattr(self, field_name, cls().from_dict(value[key]))
-                    else:
-                        # NOTE: `from_dict` mutates the underlying message, so no
-                        # assignment here is necessary.
-                        v.from_dict(value[key])
-                elif meta.map_types and meta.map_types[1] == TYPE_MESSAGE:
-                    v = getattr(self, field_name)
-                    cls = self._betterproto.cls_by_field[f"{field_name}.value"]
-                    for k in value[key]:
-                        v[k] = cls().from_dict(value[key][k])
-                else:
-                    v = value[key]
-                    if meta.proto_type in INT_64_TYPES:
-                        if isinstance(value[key], list):
-                            v = [int(n) for n in value[key]]
-                        else:
-                            v = int(value[key])
-                    elif meta.proto_type == TYPE_BYTES:
-                        if isinstance(value[key], list):
-                            v = [b64decode(n) for n in value[key]]
-                        else:
-                            v = b64decode(value[key])
-                    elif meta.proto_type == TYPE_ENUM:
-                        enum_cls = self._betterproto.cls_by_field[field_name]
-                        if isinstance(v, list):
-                            v = [enum_cls.from_string(e) for e in v]
-                        elif isinstance(v, str):
-                            v = enum_cls.from_string(v)
-                    elif meta.proto_type in (TYPE_FLOAT, TYPE_DOUBLE):
-                        if isinstance(value[key], list):
-                            v = [_parse_float(n) for n in value[key]]
-                        else:
-                            v = _parse_float(value[key])
-
-                if v is not None:
-                    setattr(self, field_name, v)
+        for field, value in self._from_dict_init(value).items():
+            setattr(self, field, value)
         return self
 
     def to_json(
@@ -1809,8 +1838,8 @@ class Message(ABC):
 
     @classmethod
     def _validate_field_groups(cls, values):
-        group_to_one_ofs = cls._betterproto_meta.oneof_field_by_group  # type: ignore
-        field_name_to_meta = cls._betterproto_meta.meta_by_field_name  # type: ignore
+        group_to_one_ofs = cls._betterproto.oneof_field_by_group
+        field_name_to_meta = cls._betterproto.meta_by_field_name
 
         for group, field_set in group_to_one_ofs.items():
             if len(field_set) == 1:
@@ -1837,6 +1866,9 @@ class Message(ABC):
         return values
 
 
+Message.__annotations__ = {}  # HACK to avoid typing.get_type_hints breaking :)
+
+
 def serialized_on_wire(message: Message) -> bool:
     """
     If this message was or should be serialized on the wire. This can be used to detect

src/betterproto/utils.py

@@ -0,0 +1,56 @@
+from __future__ import annotations
+
+from typing import (
+    Any,
+    Callable,
+    Generic,
+    Optional,
+    Type,
+    TypeVar,
+)
+
+from typing_extensions import (
+    Concatenate,
+    ParamSpec,
+    Self,
+)
+
+
+SelfT = TypeVar("SelfT")
+P = ParamSpec("P")
+HybridT = TypeVar("HybridT", covariant=True)
+
+
+class hybridmethod(Generic[SelfT, P, HybridT]):
+    def __init__(
+        self,
+        func: Callable[
+            Concatenate[type[SelfT], P], HybridT
+        ],  # Must be the classmethod version
+    ):
+        self.cls_func = func
+        self.__doc__ = func.__doc__
+
+    def instancemethod(self, func: Callable[Concatenate[SelfT, P], HybridT]) -> Self:
+        self.instance_func = func
+        return self
+
+    def __get__(
+        self, instance: Optional[SelfT], owner: Type[SelfT]
+    ) -> Callable[P, HybridT]:
+        if instance is None or self.instance_func is None:
+            # either bound to the class, or no instance method available
+            return self.cls_func.__get__(owner, None)
+        return self.instance_func.__get__(instance, owner)
+
+
+T_co = TypeVar("T_co")
+TT_co = TypeVar("TT_co", bound="type[Any]")
+
+
+class classproperty(Generic[TT_co, T_co]):
+    def __init__(self, func: Callable[[TT_co], T_co]):
+        self.__func__ = func
+
+    def __get__(self, instance: Any, type: TT_co) -> T_co:
+        return self.__func__(type)