PEP 646 implementation (#963)

typing_extensions/CHANGELOG

@@ -1,5 +1,7 @@
 # Release 4.x.x
 
+- Runtime support for PEP 646, adding `typing_extensions.TypeVarTuple`
+  and `typing_extensions.Unpack`.
 - Add interaction of `Required` and `NotRequired` with `__required_keys__`,
   `__optional_keys__` and `get_type_hints()`. Patch by David Cabot (@d-k-bo).
 - Runtime support for PEP 675 and `typing_extensions.LiteralString`.

typing_extensions/README.rst

@@ -48,6 +48,8 @@ This module currently contains the following:
   - ``Never``
   - ``reveal_type``
   - ``Self`` (see PEP 673)
+  - ``TypeVarTuple`` (see PEP 646)
+  - ``Unpack`` (see PEP 646)
 
 - In ``typing`` since Python 3.10
 
@@ -124,9 +126,15 @@ These changes are _not_ backported to prevent subtle compatibility
 issues when mixing the differing implementations of modified classes.
 
 Certain types have incorrect runtime behavior due to limitations of older
-versions of the typing module.  For example, ``ParamSpec`` and ``Concatenate``
-will not work with ``get_args``, ``get_origin``. Certain PEP 612 special cases
-in user-defined ``Generic``\ s are also not available.
+versions of the typing module:
+
+- ``ParamSpec`` and ``Concatenate`` will not work with ``get_args`` and
+  ``get_origin``. Certain PEP 612 special cases in user-defined
+  ``Generic``\ s are also not available.
+- ``Unpack`` from PEP 646 does not work properly with user-defined
+  ``Generic``\ s in Python 3.6: ``class X(Generic[Unpack[Ts]]):`` does
+  not work.
+
 These types are only guaranteed to work for static type checking.
 
 Running tests

typing_extensions/src/test_typing_extensions.py

@@ -22,7 +22,7 @@
 from typing_extensions import TypeAlias, ParamSpec, Concatenate, ParamSpecArgs, ParamSpecKwargs, TypeGuard
 from typing_extensions import Awaitable, AsyncIterator, AsyncContextManager, Required, NotRequired
 from typing_extensions import Protocol, runtime, runtime_checkable, Annotated, overload, final, is_typeddict
-from typing_extensions import dataclass_transform, reveal_type, Never, assert_never, LiteralString
+from typing_extensions import TypeVarTuple, Unpack, dataclass_transform, reveal_type, Never, assert_never, LiteralString
 try:
     from typing_extensions import get_type_hints
 except ImportError:
@@ -622,6 +622,7 @@ def test_get_origin(self):
 
         T = TypeVar('T')
         P = ParamSpec('P')
+        Ts = TypeVarTuple('Ts')
         class C(Generic[T]): pass
         self.assertIs(get_origin(C[int]), C)
         self.assertIs(get_origin(C[T]), C)
@@ -642,11 +643,16 @@ class C(Generic[T]): pass
         self.assertIs(get_origin(list), None)
         self.assertIs(get_origin(P.args), P)
         self.assertIs(get_origin(P.kwargs), P)
+        self.assertIs(get_origin(Required[int]), Required)
+        self.assertIs(get_origin(NotRequired[int]), NotRequired)
+        self.assertIs(get_origin(Unpack[Ts]), Unpack)
+        self.assertIs(get_origin(Unpack), None)
 
     def test_get_args(self):
         from typing_extensions import get_args
 
         T = TypeVar('T')
+        Ts = TypeVarTuple('Ts')
         class C(Generic[T]): pass
         self.assertEqual(get_args(C[int]), (int,))
         self.assertEqual(get_args(C[T]), (T,))
@@ -687,6 +693,10 @@ class C(Generic[T]): pass
         self.assertIn(get_args(Callable[P, int]), [(P, int), ([P], int)])
         self.assertEqual(get_args(Callable[Concatenate[int, P], int]),
                          (Concatenate[int, P], int))
+        self.assertEqual(get_args(Required[int]), (int,))
+        self.assertEqual(get_args(NotRequired[int]), (int,))
+        self.assertEqual(get_args(Unpack[Ts]), (Ts,))
+        self.assertEqual(get_args(Unpack), ())
 
 
 class CollectionsAbcTests(BaseTestCase):
@@ -2438,6 +2448,141 @@ def test_pickle(self):
             self.assertIs(Self, pickle.loads(pickled))
 
 
+class UnpackTests(BaseTestCase):
+    def test_basic_plain(self):
+        Ts = TypeVarTuple('Ts')
+        self.assertEqual(Unpack[Ts], Unpack[Ts])
+        with self.assertRaises(TypeError):
+            Unpack()
+
+    def test_repr(self):
+        Ts = TypeVarTuple('Ts')
+        self.assertEqual(repr(Unpack[Ts]), 'typing_extensions.Unpack[Ts]')
+
+    def test_cannot_subclass_vars(self):
+        with self.assertRaises(TypeError):
+            class V(Unpack[TypeVarTuple('Ts')]):
+                pass
+
+    def test_tuple(self):
+        Ts = TypeVarTuple('Ts')
+        Tuple[Unpack[Ts]]
+
+    def test_union(self):
+        Xs = TypeVarTuple('Xs')
+        Ys = TypeVarTuple('Ys')
+        self.assertEqual(
+            Union[Unpack[Xs]],
+            Unpack[Xs]
+        )
+        self.assertNotEqual(
+            Union[Unpack[Xs]],
+            Union[Unpack[Xs], Unpack[Ys]]
+        )
+        self.assertEqual(
+            Union[Unpack[Xs], Unpack[Xs]],
+            Unpack[Xs]
+        )
+        self.assertNotEqual(
+            Union[Unpack[Xs], int],
+            Union[Unpack[Xs]]
+        )
+        self.assertNotEqual(
+            Union[Unpack[Xs], int],
+            Union[int]
+        )
+        self.assertEqual(
+            Union[Unpack[Xs], int].__args__,
+            (Unpack[Xs], int)
+        )
+        self.assertEqual(
+            Union[Unpack[Xs], int].__parameters__,
+            (Xs,)
+        )
+        self.assertIs(
+            Union[Unpack[Xs], int].__origin__,
+            Union
+        )
+
+    @skipUnless(PEP_560, "Unimplemented for 3.6")
+    def test_concatenation(self):
+        Xs = TypeVarTuple('Xs')
+        self.assertEqual(Tuple[int, Unpack[Xs]].__args__, (int, Unpack[Xs]))
+        self.assertEqual(Tuple[Unpack[Xs], int].__args__, (Unpack[Xs], int))
+        self.assertEqual(Tuple[int, Unpack[Xs], str].__args__,
+                         (int, Unpack[Xs], str))
+        class C(Generic[Unpack[Xs]]): pass
+        self.assertEqual(C[int, Unpack[Xs]].__args__, (int, Unpack[Xs]))
+        self.assertEqual(C[Unpack[Xs], int].__args__, (Unpack[Xs], int))
+        self.assertEqual(C[int, Unpack[Xs], str].__args__,
+                         (int, Unpack[Xs], str))
+
+    @skipUnless(PEP_560, "Unimplemented for 3.6")
+    def test_class(self):
+        Ts = TypeVarTuple('Ts')
+
+        class C(Generic[Unpack[Ts]]): pass
+        self.assertEqual(C[int].__args__, (int,))
+        self.assertEqual(C[int, str].__args__, (int, str))
+
+        with self.assertRaises(TypeError):
+            class C(Generic[Unpack[Ts], int]): pass
+
+        T1 = TypeVar('T')
+        T2 = TypeVar('T')
+        class C(Generic[T1, T2, Unpack[Ts]]): pass
+        self.assertEqual(C[int, str].__args__, (int, str))
+        self.assertEqual(C[int, str, float].__args__, (int, str, float))
+        self.assertEqual(C[int, str, float, bool].__args__, (int, str, float, bool))
+        with self.assertRaises(TypeError):
+            C[int]
+
+
+class TypeVarTupleTests(BaseTestCase):
+
+    def test_basic_plain(self):
+        Ts = TypeVarTuple('Ts')
+        self.assertEqual(Ts, Ts)
+        self.assertIsInstance(Ts, TypeVarTuple)
+        Xs = TypeVarTuple('Xs')
+        Ys = TypeVarTuple('Ys')
+        self.assertNotEqual(Xs, Ys)
+
+    def test_repr(self):
+        Ts = TypeVarTuple('Ts')
+        self.assertEqual(repr(Ts), 'Ts')
+
+    def test_no_redefinition(self):
+        self.assertNotEqual(TypeVarTuple('Ts'), TypeVarTuple('Ts'))
+
+    def test_cannot_subclass_vars(self):
+        with self.assertRaises(TypeError):
+            class V(TypeVarTuple('Ts')):
+                pass
+
+    def test_cannot_subclass_var_itself(self):
+        with self.assertRaises(TypeError):
+            class V(TypeVarTuple):
+                pass
+
+    def test_cannot_instantiate_vars(self):
+        Ts = TypeVarTuple('Ts')
+        with self.assertRaises(TypeError):
+            Ts()
+
+    def test_tuple(self):
+        Ts = TypeVarTuple('Ts')
+        # Not legal at type checking time but we can't really check against it.
+        Tuple[Ts]
+
+    def test_args_and_parameters(self):
+        Ts = TypeVarTuple('Ts')
+
+        t = Tuple[tuple(Ts)]
+        self.assertEqual(t.__args__, (Ts.__unpacked__,))
+        self.assertEqual(t.__parameters__, (Ts,))
+
+
 class FinalDecoratorTests(BaseTestCase):
     def test_final_unmodified(self):
         def func(x): ...