bpo-29262: Add get_origin() and get_args() introspection helpers to typing (GH-13685)
This is an old feature request that appears from time to time. After a year of experimenting with various introspection capabilities in `typing_inspect` on PyPI, I propose to add these two most commonly used functions: `get_origin()` and `get_args()`. These are essentially thin public wrappers around private APIs: `__origin__` and `__args__`. As discussed in the issue and on the typing tracker, exposing some public helpers instead of `__origin__` and `__args__` directly will give us more flexibility if we will decide to update the internal representation, while still maintaining backwards compatibility. The implementation is very simple an is essentially a copy from `typing_inspect` with one exception: `ClassVar` was special-cased in `typing_inspect`, but I think this special-casing doesn't really help and only makes things more complicated.
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@ -1021,6 +1021,25 @@ The module defines the following classes, functions and decorators:
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a dictionary constructed by merging all the ``__annotations__`` along
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``C.__mro__`` in reverse order.
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.. function:: get_origin(typ)
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.. function:: get_args(typ)
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Provide basic introspection for generic types and special typing forms.
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For a typing object of the form ``X[Y, Z, ...]`` these functions return
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``X`` and ``(Y, Z, ...)``. If ``X`` is a generic alias for a builtin or
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:mod:`collections` class, it gets normalized to the original class.
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For unsupported objects return ``None`` and ``()`` correspondingly.
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Examples::
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assert get_origin(Dict[str, int]) is dict
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assert get_args(Dict[int, str]) == (int, str)
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assert get_origin(Union[int, str]) is Union
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assert get_args(Union[int, str]) == (int, str)
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.. versionadded:: 3.8
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.. decorator:: overload
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The ``@overload`` decorator allows describing functions and methods
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@ -15,6 +15,7 @@ from typing import Callable
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from typing import Generic, ClassVar, Final, final, Protocol
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from typing import cast, runtime_checkable
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from typing import get_type_hints
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from typing import get_origin, get_args
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from typing import no_type_check, no_type_check_decorator
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from typing import Type
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from typing import NewType
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@ -2735,6 +2736,42 @@ class GetTypeHintTests(BaseTestCase):
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self.assertEqual(gth(G), {'lst': ClassVar[List[T]]})
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class GetUtilitiesTestCase(TestCase):
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def test_get_origin(self):
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T = TypeVar('T')
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class C(Generic[T]): pass
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self.assertIs(get_origin(C[int]), C)
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self.assertIs(get_origin(C[T]), C)
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self.assertIs(get_origin(int), None)
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self.assertIs(get_origin(ClassVar[int]), ClassVar)
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self.assertIs(get_origin(Union[int, str]), Union)
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self.assertIs(get_origin(Literal[42, 43]), Literal)
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self.assertIs(get_origin(Final[List[int]]), Final)
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self.assertIs(get_origin(Generic), Generic)
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self.assertIs(get_origin(Generic[T]), Generic)
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self.assertIs(get_origin(List[Tuple[T, T]][int]), list)
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def test_get_args(self):
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T = TypeVar('T')
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class C(Generic[T]): pass
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self.assertEqual(get_args(C[int]), (int,))
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self.assertEqual(get_args(C[T]), (T,))
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self.assertEqual(get_args(int), ())
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self.assertEqual(get_args(ClassVar[int]), (int,))
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self.assertEqual(get_args(Union[int, str]), (int, str))
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self.assertEqual(get_args(Literal[42, 43]), (42, 43))
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self.assertEqual(get_args(Final[List[int]]), (List[int],))
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self.assertEqual(get_args(Union[int, Tuple[T, int]][str]),
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(int, Tuple[str, int]))
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self.assertEqual(get_args(typing.Dict[int, Tuple[T, T]][Optional[int]]),
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(int, Tuple[Optional[int], Optional[int]]))
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self.assertEqual(get_args(Callable[[], T][int]), ([], int,))
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self.assertEqual(get_args(Union[int, Callable[[Tuple[T, ...]], str]]),
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(int, Callable[[Tuple[T, ...]], str]))
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self.assertEqual(get_args(Tuple[int, ...]), (int, ...))
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self.assertEqual(get_args(Tuple[()]), ((),))
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class CollectionsAbcTests(BaseTestCase):
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def test_hashable(self):
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@ -99,6 +99,8 @@ __all__ = [
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'AnyStr',
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'cast',
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'final',
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'get_args',
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'get_origin',
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'get_type_hints',
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'NewType',
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'no_type_check',
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@ -1253,6 +1255,46 @@ def get_type_hints(obj, globalns=None, localns=None):
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return hints
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def get_origin(tp):
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"""Get the unsubscripted version of a type.
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This supports generic types, Callable, Tuple, Union, Literal, Final and ClassVar.
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Return None for unsupported types. Examples::
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get_origin(Literal[42]) is Literal
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get_origin(int) is None
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get_origin(ClassVar[int]) is ClassVar
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get_origin(Generic) is Generic
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get_origin(Generic[T]) is Generic
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get_origin(Union[T, int]) is Union
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get_origin(List[Tuple[T, T]][int]) == list
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"""
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if isinstance(tp, _GenericAlias):
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return tp.__origin__
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if tp is Generic:
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return Generic
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return None
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def get_args(tp):
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"""Get type arguments with all substitutions performed.
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For unions, basic simplifications used by Union constructor are performed.
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Examples::
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get_args(Dict[str, int]) == (str, int)
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get_args(int) == ()
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get_args(Union[int, Union[T, int], str][int]) == (int, str)
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get_args(Union[int, Tuple[T, int]][str]) == (int, Tuple[str, int])
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get_args(Callable[[], T][int]) == ([], int)
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"""
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if isinstance(tp, _GenericAlias):
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res = tp.__args__
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if get_origin(tp) is collections.abc.Callable and res[0] is not Ellipsis:
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res = (list(res[:-1]), res[-1])
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return res
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return ()
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def no_type_check(arg):
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"""Decorator to indicate that annotations are not type hints.
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@ -0,0 +1 @@
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Add ``get_origin()`` and ``get_args()`` introspection helpers to ``typing`` module.
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