Improve types

toot/entities.py

@@ -14,12 +14,18 @@ import typing as t
 from dataclasses import dataclass, is_dataclass
 from datetime import date, datetime
 from functools import lru_cache
-from typing import Any, Dict, Optional, Tuple, Type, TypeVar, Union
+from typing import Any, Dict, NamedTuple, Optional, Type, TypeVar, Union
 from typing import get_args, get_origin, get_type_hints
 
 from toot.utils import get_text
 from toot.utils.datetime import parse_datetime
 
+# Generic data class instance
+T = TypeVar("T")
+
+# A dict decoded from JSON
+Data = Dict[str, Any]
+
 
 @dataclass
 class AccountField:
@@ -76,7 +82,7 @@ class Account:
     source: Optional[dict]
 
     @staticmethod
-    def __toot_prepare__(obj: Dict) -> Dict:
+    def __toot_prepare__(obj: Data) -> Data:
         # Pleroma has not yet converted last_status_at from datetime to date
         # so trim it here so it doesn't break when converting to date.
         # See: https://git.pleroma.social/pleroma/pleroma/-/issues/1470
@@ -266,7 +272,7 @@ class Status:
         return self.reblog or self
 
     @staticmethod
-    def __toot_prepare__(obj: Dict) -> Dict:
+    def __toot_prepare__(obj: Data) -> Data:
         # Pleroma has a bug where created_at is set to an empty string.
         # To avoid marking created_at as optional, which would require work
         # because we count on it always existing, set it to current datetime.
@@ -457,27 +463,25 @@ class List:
     # see: https://git.pleroma.social/pleroma/pleroma/-/issues/2918
     replies_policy: Optional[str]
 
+# ------------------------------------------------------------------------------
 
-# Generic data class instance
+
-T = TypeVar("T")
+class Field(NamedTuple):
+    name: str
+    type: Any
+    default: Any
 
 
 class ConversionError(Exception):
     """Raised when conversion fails from JSON value to data class field."""
-    def __init__(
+    def __init__(self, data_class: type, field: Field, field_value: Optional[str]):
-        self,
-        data_class: Type,
-        field_name: str,
-        field_type: Type,
-        field_value: Optional[str]
-    ):
         super().__init__(
-            f"Failed converting field `{data_class.__name__}.{field_name}` "
+            f"Failed converting field `{data_class.__name__}.{field.name}` "
-            + f"of type `{field_type.__name__}` from value {field_value!r}"
+            + f"of type `{field.type.__name__}` from value {field_value!r}"
         )
 
 
-def from_dict(cls: Type[T], data: Dict) -> T:
+def from_dict(cls: Type[T], data: Data) -> T:
     """Convert a nested dict into an instance of `cls`."""
     # Apply __toot_prepare__ if it exists
     prepare = getattr(cls, '__toot_prepare__', None)
@@ -485,19 +489,19 @@ def from_dict(cls: Type[T], data: Dict) -> T:
         data = prepare(data)
 
     def _fields():
-        for name, type, default in get_fields(cls):
+        for field in _get_fields(cls):
-            value = data.get(name, default)
+            value = data.get(field.name, field.default)
-            converted = _convert_with_error_handling(cls, name, type, value)
+            converted = _convert_with_error_handling(cls, field, value)
-            yield name, converted
+            yield field.name, converted
 
     return cls(**dict(_fields()))
 
 
-@lru_cache(maxsize=100)
+@lru_cache
-def get_fields(cls: Type) -> t.List[Tuple[str, Type, Any]]:
+def _get_fields(cls: type) -> t.List[Field]:
     hints = get_type_hints(cls)
     return [
-        (
+        Field(
             field.name,
             _prune_optional(hints[field.name]),
             _get_default_value(field)
@@ -506,11 +510,11 @@ def get_fields(cls: Type) -> t.List[Tuple[str, Type, Any]]:
     ]
 
 
-def from_dict_list(cls: Type[T], data: t.List[Dict]) -> t.List[T]:
+def from_dict_list(cls: Type[T], data: t.List[Data]) -> t.List[T]:
     return [from_dict(cls, x) for x in data]
 
 
-def _get_default_value(field):
+def _get_default_value(field: dataclasses.Field[Any]):
     if field.default is not dataclasses.MISSING:
         return field.default
 
@@ -520,21 +524,16 @@ def _get_default_value(field):
     return None
 
 
-def _convert_with_error_handling(
+def _convert_with_error_handling(data_class: type, field: Field, field_value: Any) -> Any:
-    data_class: Type,
-    field_name: str,
-    field_type: Type,
-    field_value: Optional[str]
-):
     try:
-        return _convert(field_type, field_value)
+        return _convert(field.type, field_value)
     except ConversionError:
         raise
     except Exception:
-        raise ConversionError(data_class, field_name, field_type, field_value)
+        raise ConversionError(data_class, field, field_value)
 
 
-def _convert(field_type, value):
+def _convert(field_type: Any, value: Any) -> Any:
     if value is None:
         return None
 
@@ -557,7 +556,7 @@ def _convert(field_type, value):
     raise ValueError(f"Not implemented for type '{field_type}'")
 
 
-def _prune_optional(field_type: Type) -> Type:
+def _prune_optional(field_type: type) -> type:
     """For `Optional[<type>]` returns the encapsulated `<type>`."""
     if get_origin(field_type) == Union:
         args = get_args(field_type)