Remove typing.cast

delfick · delfick · commit 2ff359e460c5 · 2025-05-11T11:06:48.000+10:00
It's too easy to misunderstand that typing.cast is not a runtime thing.
Much more obvious with a type ignore comment
diff --git a/strcs/annotations.py b/strcs/annotations.py
@@ -19,7 +19,7 @@
 object as a creator override.
 """
 
-from typing import TYPE_CHECKING, Generic, Protocol, TypeVar, cast, runtime_checkable
+from typing import TYPE_CHECKING, Generic, Protocol, TypeVar, runtime_checkable
 
 import attrs
 
@@ -305,7 +305,7 @@ def adjusted_creator(
         type_cache: TypeCache,
     ) -> ConvertFunction[T] | None:
         def retrieve(value: object, /, _meta: Meta) -> ConvertResponse[T]:
-            return cast(T, _meta.retrieve_one(object, "retrieved", type_cache=type_cache))
+            return _meta.retrieve_one(object, "retrieved", type_cache=type_cache)  # type: ignore[return-value]
 
         a = Ann[T](creator=retrieve)
         return a.adjusted_creator(creator, register, typ, type_cache)
diff --git a/strcs/decorator.py b/strcs/decorator.py
@@ -72,7 +72,7 @@ def create_thing(value: object, /) -> strcs.ConvertResponse[Thing]:
 
 import inspect
 from collections.abc import Callable, Generator, Mapping
-from typing import TYPE_CHECKING, Generic, TypeVar, cast
+from typing import TYPE_CHECKING, Generic, TypeVar
 
 import attrs
 import cattrs
@@ -197,7 +197,7 @@ def __call__(self, create_args: "CreateArgs") -> T:
 
         if self.assume_unchanged_converted and want.is_type_for(value):
             if want.origin_type not in builtin_types:
-                return cast(T, value)
+                return value  # type: ignore[return-value]
 
         try:
             args = ArgsExtractor(
@@ -260,7 +260,7 @@ def deal(res: ConvertResponse[T], value: object) -> T:
                         reason="Told to use NotSpecified as the final value",
                         creator=self.func,
                     )
-                return cast(T, value)
+                return value  # type: ignore[return-value]
             else:
                 if not isinstance(res, Mapping) and issubclass(
                     want.checkable, self.type_cache.disassemble(type(res)).checkable
diff --git a/strcs/disassemble/_base.py b/strcs/disassemble/_base.py
@@ -14,7 +14,6 @@
     TypeGuard,
     TypeVar,
     Union,
-    cast,
     overload,
 )
 
@@ -139,7 +138,7 @@ def create(
         original = typ
 
         if isinstance(typ, cls):
-            return cast(Type[U], typ)
+            return typ  # type: ignore[return-value]
 
         if typ in cache:
             return cache[original]
@@ -160,7 +159,7 @@ def create(
             type_alias = extracted
             extracted = extracted.__supertype__
 
-        constructor = cast(Callable[..., Type[U]], cls)
+        constructor: Callable[..., Type[U]] = cls  # type: ignore[assignment]
 
         made = constructor(
             cache=cache,
@@ -723,7 +722,7 @@ def checkable_as_type(self) -> type[T]:
         Return ``self.checkable``, but the return type of this function is a
         python type of the inner type represented by this :class:`strcs.Type`
         """
-        return cast(type[T], self.checkable)
+        return self.checkable  # type: ignore[return-value]
 
     @memoized_property
     def checkable(self) -> type[InstanceCheck]:
diff --git a/strcs/disassemble/_comparer.py b/strcs/disassemble/_comparer.py
@@ -1,7 +1,7 @@
 import functools
 import operator
 import typing
-from typing import TYPE_CHECKING, Annotated, NewType, Optional, cast
+from typing import TYPE_CHECKING, Annotated, NewType, Optional
 
 import attrs
 
@@ -27,7 +27,7 @@ class Distilled:
     def classinfo(self) -> type | tuple[type, ...]:
         if not self.is_valid:
             raise NotValidType()
-        return cast(type | tuple[type, ...], self.original)
+        return self.original  # type: ignore[return-value]
 
     @property
     def as_tuple(self) -> tuple[type, ...]:
diff --git a/strcs/disassemble/_creation.py b/strcs/disassemble/_creation.py
@@ -1,5 +1,5 @@
 from collections.abc import Mapping, MutableMapping
-from typing import TypeVar, cast
+from typing import TypeVar
 
 import attrs
 import cattrs
@@ -49,7 +49,7 @@ def instantiate(want: Type[T], res: object, converter: cattrs.Converter) -> T:
     """
     if res is None:
         if want.optional or want.original is None:
-            return cast(T, None)
+            return None  # type: ignore[return-value]
 
         raise ValueError("Can't instantiate object with None")
 
@@ -70,7 +70,7 @@ def instantiate(want: Type[T], res: object, converter: cattrs.Converter) -> T:
             continue
 
         val = res[name]
-        attribute = cast(attrs.Attribute, field)
+        attribute: attrs.Attribute = field  # type: ignore[assignment]
         conv_obj[name] = converter._structure_attribute(attribute, val)
 
     return instantiator(**conv_obj)
diff --git a/strcs/hints.py b/strcs/hints.py
@@ -23,7 +23,6 @@
     TypeGuard,
     TypeVar,
     Union,
-    cast,
     runtime_checkable,
 )
 
@@ -302,7 +301,8 @@ class Other:
         else:
             return cls
 
-        cast(WithResolvedTypes[C], cls).__strcs_types_resolved__ = cls
+        with_resolved_types: WithResolvedTypes[C] = cls  # type: ignore[assignment]
+        with_resolved_types.__strcs_types_resolved__ = cls
 
         # Copied from standard library typing.get_type_hints
         # Cause I need globals/locals to resolve nested types that don't have forwardrefs
diff --git a/strcs/hooks.py b/strcs/hooks.py
@@ -7,7 +7,7 @@
 for specific properties on a class.
 """
 
-from typing import TYPE_CHECKING, TypeVar, cast
+from typing import TYPE_CHECKING, TypeVar
 
 import cattrs
 
@@ -208,4 +208,7 @@ def bypass(self, value: object, want: Type[T]) -> T:
             self.converter._structure_func.dispatch.cache_clear()
         if isinstance(value, dict):
             value = fill(want, value)
-        return self.converter.structure(value, cast(type, want.original))
+        return self.converter.structure(
+            value,
+            want.original,  # type: ignore[arg-type]
+        )
diff --git a/strcs/memoized_property.py b/strcs/memoized_property.py
@@ -1,5 +1,5 @@
 from collections.abc import Callable, MutableMapping
-from typing import Generic, TypeVar, Union, cast, overload
+from typing import Generic, TypeVar, Union, overload
 
 PropRet = TypeVar("PropRet")
 
@@ -66,7 +66,7 @@ def __get__(
         if self.name not in cache:
             cache[self.name] = self.func(instance)
 
-        return cast(PropRet, cache[self.name])
+        return cache[self.name]  # type: ignore[return-value]
 
     def __delete__(self, instance: object) -> None:
         cache = self.cache(instance)
diff --git a/strcs/meta.py b/strcs/meta.py
@@ -1,7 +1,7 @@
 import fnmatch
 import inspect
 from collections.abc import Iterable, Mapping
-from typing import Protocol, TypeVar, cast, overload
+from typing import Protocol, TypeVar, overload
 
 import attrs
 import cattrs
@@ -117,7 +117,7 @@ def narrow(self, *patterns: str, obj: Mapping | object = Empty) -> dict[str, obj
                 pattern = pattern[1:]
             for n in self.keys_from(obj):
                 if progress.obj_is_mapping:
-                    v = cast(Mapping, obj)[n]
+                    v = obj[n]  # type: ignore[index]
                 else:
                     v = getattr(obj, n)
 
@@ -202,7 +202,7 @@ def find_by_type(
         if data is Empty:
             data = self.data
 
-        data = cast(dict[str, object], data)
+        data: dict[str, object] = data  # type: ignore[assignment]
 
         if typ is object:
             return False, data
@@ -288,15 +288,15 @@ def retrieve_one(
             if with_patterns or typ is object:
                 data = with_patterns
             elif default is not inspect._empty:
-                return cast(T, default)
+                return default  # type: ignore[return-value]
 
         optional, found = self.find_by_type(typ, data=data, type_cache=type_cache)
 
         if patterns and data and not found and not optional:
             raise errors.FoundWithWrongType(patterns=list(patterns), want=typ)
 
         if optional and not found:
-            return cast(T, None)
+            return None  # type: ignore[return-value]
 
         if len(found) == 1:
             for thing in found.values():
@@ -306,7 +306,7 @@ def retrieve_one(
             raise errors.MultipleNamesForType(want=typ, found=sorted(found))
 
         if default is not inspect._empty:
-            return cast(T, default)
+            return default  # type: ignore[return-value]
 
         raise errors.NoDataByTypeName(
             want=typ,
diff --git a/strcs/register.py b/strcs/register.py
@@ -3,7 +3,7 @@
 specific types.
 """
 
-from typing import Annotated, ClassVar, Generic, Protocol, TypeVar, cast
+from typing import Annotated, ClassVar, Generic, Protocol, TypeVar
 
 import cattrs
 
@@ -173,12 +173,12 @@ def __call__(
                     typ = self.original
 
                 self.wrapped = WrappedCreator[T](
-                    cast(Type[T], typ),
+                    typ,  # type: ignore[arg-type]
                     func,
                     type_cache=register.type_cache,
                     assume_unchanged_converted=self.assume_unchanged_converted,
                 )
-                self.typ = cast(Type[T], typ)
+                self.typ = typ  # type: ignore[assignment]
                 self.func = self.wrapped.func
 
                 register[typ] = self.wrapped
@@ -238,10 +238,11 @@ def create_annotated(
         This is the same as ``reg.create`` but the type will be wrapped with the
         provided annotation.
         """
+        want: Type[T]
         if isinstance(typ, Type):
             want = typ
         else:
-            want = cast(Type[T], self.type_cache.disassemble(Annotated[typ, ann]))
+            want = self.type_cache.disassemble(Annotated[typ, ann])  # type: ignore[assignment]
 
         return CreateStructureHook.structure(
             register=self,
diff --git a/tests/disassemble/test_helpers.py b/tests/disassemble/test_helpers.py
@@ -1,7 +1,7 @@
 import dataclasses
 import inspect
-from collections.abc import Callable, Sequence
-from typing import Annotated, Optional, cast
+from collections.abc import Sequence
+from typing import Annotated, Optional
 
 import attrs
 import pytest
@@ -365,7 +365,7 @@ class Thing:
             ],
         )
 
-        thing = cast(Callable, Thing)(stuff="one", wat="blah", blah=3)
+        thing = Thing(stuff="one", wat="blah", blah=3)
         assert thing.stuff == "one"
         assert thing._thing == "blah"
         assert thing.other == 3
diff --git a/tests/disassemble/test_instance_check.py b/tests/disassemble/test_instance_check.py
@@ -3,7 +3,7 @@
 import types
 import typing
 from collections.abc import Callable
-from typing import Annotated, Generic, NewType, TypeVar, Union, cast
+from typing import Annotated, Generic, NewType, TypeVar, Union
 
 import attrs
 import pytest
@@ -375,7 +375,7 @@ def test_it_can_find_instances_and_subclasses_of_primtive_NewType_objects(
 
     def test_it_can_instantiate_the_provided_type(self, Dis: Disassembler):
         checkable = Dis(dict[str, bool]).checkable
-        made = cast(Callable, checkable)([("1", True), ("2", False)])
+        made = checkable([("1", True), ("2", False)])  # type: ignore[call-arg]
         assert made == {"1": True, "2": False}
 
         assert checkable.Meta.typ == dict
@@ -389,7 +389,7 @@ def __init__(self, one: int):
                 self.one = one
 
         checkable = Dis(Thing).checkable
-        made = cast(Callable, checkable)(one=1)
+        made = checkable(one=1)  # type: ignore[call-arg]
         assert isinstance(made, Thing)
         assert made.one == 1
 
diff --git a/tests/test_hints.py b/tests/test_hints.py
@@ -1,6 +1,6 @@
 import dataclasses
 from collections.abc import Callable, Iterable
-from typing import Annotated, Optional, Protocol, cast
+from typing import Annotated, Optional, Protocol
 
 import attrs
 
@@ -26,7 +26,13 @@ class TestResolveTypes:
     def test_it_just_returns_the_object_if_its_not_an_attrs_dataclass_class(self) -> None:
         thing: object
         for thing in (None, 0, 1, [], [1], {}, {1: 2}, True, False, lambda: 1):
-            assert strcs.resolve_types(cast(type, thing), type_cache=strcs.TypeCache()) is thing
+            assert (
+                strcs.resolve_types(  # type: ignore[type-var]
+                    thing,  # type: ignore[arg-type]
+                    type_cache=strcs.TypeCache(),
+                )
+                is thing
+            )
 
     def test_it_clears_the_type_cache(self) -> None:
         type_cache = strcs.TypeCache()
diff --git a/tests/test_register.py b/tests/test_register.py
