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.
This commit is contained in:
Ivan Levkivskyi 2019-05-31 00:10:07 +01:00 committed by GitHub
parent 2a58b0636d
commit 4c23aff065
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4 changed files with 99 additions and 0 deletions

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@ -1021,6 +1021,25 @@ The module defines the following classes, functions and decorators:
a dictionary constructed by merging all the ``__annotations__`` along
``C.__mro__`` in reverse order.
.. function:: get_origin(typ)
.. function:: get_args(typ)
Provide basic introspection for generic types and special typing forms.
For a typing object of the form ``X[Y, Z, ...]`` these functions return
``X`` and ``(Y, Z, ...)``. If ``X`` is a generic alias for a builtin or
:mod:`collections` class, it gets normalized to the original class.
For unsupported objects return ``None`` and ``()`` correspondingly.
Examples::
assert get_origin(Dict[str, int]) is dict
assert get_args(Dict[int, str]) == (int, str)
assert get_origin(Union[int, str]) is Union
assert get_args(Union[int, str]) == (int, str)
.. versionadded:: 3.8
.. decorator:: overload
The ``@overload`` decorator allows describing functions and methods

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@ -15,6 +15,7 @@ from typing import Callable
from typing import Generic, ClassVar, Final, final, Protocol
from typing import cast, runtime_checkable
from typing import get_type_hints
from typing import get_origin, get_args
from typing import no_type_check, no_type_check_decorator
from typing import Type
from typing import NewType
@ -2735,6 +2736,42 @@ class GetTypeHintTests(BaseTestCase):
self.assertEqual(gth(G), {'lst': ClassVar[List[T]]})
class GetUtilitiesTestCase(TestCase):
def test_get_origin(self):
T = TypeVar('T')
class C(Generic[T]): pass
self.assertIs(get_origin(C[int]), C)
self.assertIs(get_origin(C[T]), C)
self.assertIs(get_origin(int), None)
self.assertIs(get_origin(ClassVar[int]), ClassVar)
self.assertIs(get_origin(Union[int, str]), Union)
self.assertIs(get_origin(Literal[42, 43]), Literal)
self.assertIs(get_origin(Final[List[int]]), Final)
self.assertIs(get_origin(Generic), Generic)
self.assertIs(get_origin(Generic[T]), Generic)
self.assertIs(get_origin(List[Tuple[T, T]][int]), list)
def test_get_args(self):
T = TypeVar('T')
class C(Generic[T]): pass
self.assertEqual(get_args(C[int]), (int,))
self.assertEqual(get_args(C[T]), (T,))
self.assertEqual(get_args(int), ())
self.assertEqual(get_args(ClassVar[int]), (int,))
self.assertEqual(get_args(Union[int, str]), (int, str))
self.assertEqual(get_args(Literal[42, 43]), (42, 43))
self.assertEqual(get_args(Final[List[int]]), (List[int],))
self.assertEqual(get_args(Union[int, Tuple[T, int]][str]),
(int, Tuple[str, int]))
self.assertEqual(get_args(typing.Dict[int, Tuple[T, T]][Optional[int]]),
(int, Tuple[Optional[int], Optional[int]]))
self.assertEqual(get_args(Callable[[], T][int]), ([], int,))
self.assertEqual(get_args(Union[int, Callable[[Tuple[T, ...]], str]]),
(int, Callable[[Tuple[T, ...]], str]))
self.assertEqual(get_args(Tuple[int, ...]), (int, ...))
self.assertEqual(get_args(Tuple[()]), ((),))
class CollectionsAbcTests(BaseTestCase):
def test_hashable(self):

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@ -99,6 +99,8 @@ __all__ = [
'AnyStr',
'cast',
'final',
'get_args',
'get_origin',
'get_type_hints',
'NewType',
'no_type_check',
@ -1253,6 +1255,46 @@ def get_type_hints(obj, globalns=None, localns=None):
return hints
def get_origin(tp):
"""Get the unsubscripted version of a type.
This supports generic types, Callable, Tuple, Union, Literal, Final and ClassVar.
Return None for unsupported types. Examples::
get_origin(Literal[42]) is Literal
get_origin(int) is None
get_origin(ClassVar[int]) is ClassVar
get_origin(Generic) is Generic
get_origin(Generic[T]) is Generic
get_origin(Union[T, int]) is Union
get_origin(List[Tuple[T, T]][int]) == list
"""
if isinstance(tp, _GenericAlias):
return tp.__origin__
if tp is Generic:
return Generic
return None
def get_args(tp):
"""Get type arguments with all substitutions performed.
For unions, basic simplifications used by Union constructor are performed.
Examples::
get_args(Dict[str, int]) == (str, int)
get_args(int) == ()
get_args(Union[int, Union[T, int], str][int]) == (int, str)
get_args(Union[int, Tuple[T, int]][str]) == (int, Tuple[str, int])
get_args(Callable[[], T][int]) == ([], int)
"""
if isinstance(tp, _GenericAlias):
res = tp.__args__
if get_origin(tp) is collections.abc.Callable and res[0] is not Ellipsis:
res = (list(res[:-1]), res[-1])
return res
return ()
def no_type_check(arg):
"""Decorator to indicate that annotations are not type hints.

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@ -0,0 +1 @@
Add ``get_origin()`` and ``get_args()`` introspection helpers to ``typing`` module.