Drop support for mypy_extensions.TypedDict

Resolves #23

Author: davidfstr

.github/copilot-instructions.md

@@ -22,7 +22,7 @@ Single-file implementation in `trycast/__init__.py` (~1300 lines).
   else:
       from typing import _eval_type as eval_type
   ```
-- TypedDict compatibility: prefer `typing.TypedDict`, fallback to `typing_extensions.TypedDict`, avoid `mypy_extensions.TypedDict`
+- TypedDict compatibility: prefer `typing.TypedDict`, fallback to `typing_extensions.TypedDict`
 
 ### Debugging CPython typing.py Changes
 

README.md

@@ -219,7 +219,6 @@ python -m pip install trycast
   not-required keys correctly:
     * Use Python 3.9+.
     * Prefer using `typing.TypedDict` instead of `typing_extensions.TypedDict`.
-    * Avoid using `mypy_extensions.TypedDict` in general.
 
 
 ## Presentations & Videos
@@ -307,7 +306,6 @@ make help
 * TypedDict
     * typing.TypedDict, typing_extensions.TypedDict
       ([PEP 589](https://peps.python.org/pep-0589/))
-    * mypy_extensions.TypedDict (when strict=False)
     * –––
     * Required, NotRequired
       ([PEP 655](https://peps.python.org/pep-0655/))
@@ -399,12 +397,6 @@ also be a valid complex value, as consistent with Python typecheckers:
 Parameters:
 
 * **strict** -- 
-    * If strict=False then this function will additionally accept
-      mypy_extensions.TypedDict instances for the `tp` parameter. 
-      Normally these kinds of types are
-      rejected with a TypeNotSupportedError because these
-      types do not preserve enough information at runtime to reliably
-      determine which keys are required and which are potentially-missing.
     * If strict=False then `NewType("Foo", T)` will be treated
       the same as `T`. Normally NewTypes are rejected with a
       TypeNotSupportedError because values of NewTypes at runtime
@@ -417,7 +409,6 @@ Parameters:
 Raises:
 
 * **TypeNotSupportedError** --
-    * If strict=True and mypy_extensions.TypedDict is found within the `tp` argument.
     * If strict=True and a NewType is found within the `tp` argument.
     * If a TypeVar is found within the `tp` argument.
     * If an unrecognized Generic type is found within the `tp` argument.
@@ -524,9 +515,12 @@ raised exceptions, and other details.
 ### main (v2.0.0)
 
 * Drop support for Python 3.8.
-    * Remove supporting code for Python 3.8's neutered TypedDict.
+    * Drop support for Python 3.8's neutered TypedDict,
+      which lacks metadata present in later versions.
 * Drop support for Pytype type checker, since it has been 
-  [deprecated](https://github.com/google/pytype/blob/main/README.md).
+  [deprecated](https://github.com/google/pytype/blob/main/README.md)
+  as of Aug 2025.
+* Drop support for mypy_extensions.TypedDict, since it was deprecated in Aug 2023.
 
 ### v1.2.1
 

poetry.lock

@@ -33,7 +33,6 @@ python = ">=3.9"
 
 [tool.poetry.group.dev.dependencies]
 mypy = "*"
-mypy_extensions = "*"
 pyright = "*"
 pyre-check = "*"
 tox = ">=4.0.0,<5.0.0"

pyproject.toml

@@ -34,8 +34,6 @@
 from typing import TypeVar, Union, cast
 from unittest import SkipTest, TestCase
 
-import mypy_extensions
-
 import test_data.forwardrefs_example
 import test_data.forwardrefs_example_with_import_annotations
 from tests_shape_example import HTTP_400_BAD_REQUEST, draw_shape_endpoint, shapes_drawn
@@ -1853,24 +1851,8 @@ def test_types_defined_in_module_with_import_annotations(self) -> None:
         )
 
     # === strict=True mode ===
-
-    def test_rejects_mypy_typeddict_when_strict_is_true(self) -> None:
-        class Point2D(mypy_extensions.TypedDict):  # type: ignore[reportGeneralTypeIssues]  # pyright
-            x: int
-            y: int
-
-        class Point3D(Point2D, total=False):  # type: ignore[reportGeneralTypeIssues]  # pyright
-            z: int
-
-        self.assertRaisesRegex(
-            TypeNotSupportedError,
-            (
-                "trycast cannot determine which keys are required.*?"
-                "Suggest use a typing(_extensions)?.TypedDict.*?"
-                "strict=False"
-            ),
-            lambda: trycast(Point3D, {"x": 1, "y": 2}, strict=True),
-        )
+    
+    # (TODO: Add test related to NewTypes)
 
     # NOTE: Cannot combine the following two if-checks with an `and`
     #       because that is too complicated for Pyre to understand.
@@ -1899,48 +1881,8 @@ class Point3D(Point2D, total=False):
                 )
 
     # === strict=False mode ===
-
-    def test_accepts_mypy_typeddict_when_strict_is_false(self) -> None:
-        class Point2D(mypy_extensions.TypedDict):  # type: ignore[reportGeneralTypeIssues]  # pyright
-            x: int
-            y: int
-
-        # NOTE: mypy_extensions.TypedDict doesn't preserve at runtime
-        #       which of Point3D's inherited fields from Point2D are required.
-        #       So trycast() guesses (incorrectly) that ALL fields of Point3D
-        #       are not-required because Point3D is declared as total=False.
-        class Point3D(Point2D, total=False):  # type: ignore[reportGeneralTypeIssues]  # pyright
-            z: int
-
-        class MaybePoint1D(mypy_extensions.TypedDict, total=False):  # type: ignore[reportGeneralTypeIssues]  # pyright
-            x: int
-
-        class TaggedMaybePoint1D(MaybePoint1D):
-            name: str
-
-        self.assertTryCastSuccess(Point2D, {"x": 1, "y": 2}, strict=False)
-        self.assertTryCastFailure(Point2D, {"x": 1, "y": "string"}, strict=False)
-        self.assertTryCastFailure(Point2D, {"x": 1}, strict=False)
-
-        self.assertTryCastSuccess(Point3D, {"x": 1, "y": 2, "z": 3}, strict=False)
-        self.assertTryCastFailure(
-            Point3D, {"x": 1, "y": 2, "z": "string"}, strict=False
-        )
-        self.assertTryCastSuccess(Point3D, {"x": 1, "y": 2}, strict=False)
-        self.assertTryCastSuccess(Point3D, {"x": 1}, strict=False)  # surprise!
-        self.assertTryCastSuccess(Point3D, {"q": 1}, strict=False)  # surprise!
-
-        self.assertTryCastSuccess(MaybePoint1D, {"x": 1}, strict=False)
-        self.assertTryCastFailure(MaybePoint1D, {"x": "string"}, strict=False)
-        self.assertTryCastSuccess(MaybePoint1D, {}, strict=False)
-        self.assertTryCastSuccess(MaybePoint1D, {"q": 1}, strict=False)  # surprise!
-
-        self.assertTryCastSuccess(
-            TaggedMaybePoint1D, {"x": 1, "name": "one"}, strict=False
-        )
-        self.assertTryCastFailure(
-            TaggedMaybePoint1D, {"name": "one"}, strict=False
-        )  # surprise!
+    
+    # (TODO: Add test related to NewTypes)
 
     # === Misuse: Nice Error Messages ===
 
@@ -2905,11 +2847,6 @@ class TypingExtensionsPoint(TypingExtensionsTypedDict):
     y: int
 
 
-class MypyExtensionsPoint(mypy_extensions.TypedDict):  # type: ignore[reportGeneralTypeIssues]  # pyright
-    x: int
-    y: int
-
-
 class TestIsTypedDict(TestCase):
     """
     Tests whether the _is_typed_dict() internal function works.
@@ -2921,9 +2858,6 @@ def test_recognizes_typed_dict_from_typing(self) -> None:
     def test_recognizes_typed_dict_from_typing_extensions(self) -> None:
         self.assertTrue(_is_typed_dict(TypingExtensionsPoint))
 
-    def test_recognizes_typed_dict_from_mypy_extensions(self) -> None:
-        self.assertTrue(_is_typed_dict(MypyExtensionsPoint))
-
 
 # ------------------------------------------------------------------------------
 # Meta: TestTypechecks

tests.py

@@ -138,15 +138,6 @@ def __class_getitem__(cls, key):
 except ImportError:
     pass
 
-try:
-    from mypy_extensions import (  # type: ignore[attr-defined]  # isort: skip
-        _TypedDictMeta as _MypyExtensionsTypedDictMeta,  # type: ignore[reportGeneralTypeIssues]  # pyright
-    )
-
-    _typed_dict_meta_list.append(_MypyExtensionsTypedDictMeta)  # type: ignore[16]  # pyre
-except ImportError:
-    pass
-
 _typed_dict_metas = tuple(_typed_dict_meta_list)
 
 
@@ -364,12 +355,6 @@ def trycast(tp, value, /, failure=None, *, strict=True, eval=True):
 
     Parameters:
     * strict --
-        * If strict=False then this function will additionally accept
-          mypy_extensions.TypedDict instances for the `tp` parameter.
-          Normally these kinds of types are
-          rejected with a TypeNotSupportedError because these
-          types do not preserve enough information at runtime to reliably
-          determine which keys are required and which are potentially-missing.
         * If strict=False then `NewType("Foo", T)` will be treated
           the same as `T`. Normally NewTypes are rejected with a
           TypeNotSupportedError because values of NewTypes at runtime
@@ -381,7 +366,6 @@ def trycast(tp, value, /, failure=None, *, strict=True, eval=True):
 
     Raises:
     * TypeNotSupportedError --
-        * If strict=True and mypy_extensions.TypedDict is found within the `tp` argument.
         * If strict=True and a NewType is found within the `tp` argument.
         * If a TypeVar is found within the `tp` argument.
         * If an unrecognized Generic type is found within the `tp` argument.
@@ -768,24 +752,8 @@ def _checkcast_inner(
             else:
                 resolved_annotations = tp.__annotations__
 
-            try:
-                # {typing, typing_extensions}.TypedDict
-                required_keys = tp.__required_keys__  # type: ignore[attr-defined]  # mypy
-            except AttributeError:
-                # {mypy_extensions}.TypedDict
-                if options.strict:
-                    advise = "Suggest use a typing.TypedDict instead."
-                    advise2 = f"Or use {options.funcname}(..., strict=False)."
-                    raise TypeNotSupportedError(
-                        f"{options.funcname} cannot determine which keys are required "
-                        f"and which are potentially-missing for the "
-                        f"specified kind of TypedDict. {advise} {advise2}"
-                    )
-                else:
-                    if tp.__total__:  # type: ignore[attr-defined]  # mypy
-                        required_keys = resolved_annotations.keys()
-                    else:
-                        required_keys = frozenset()
+            # {typing, typing_extensions}.TypedDict
+            required_keys = tp.__required_keys__  # type: ignore[attr-defined]  # mypy
 
             for k, v in value.items():
                 V = resolved_annotations.get(k, _MISSING)