mirror of https://github.com/python/cpython
gh-118647: Add defaults to typing.Generator and typing.AsyncGenerator (#118648)
Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com> Co-authored-by: Nikita Sobolev <mail@sobolevn.me>
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@ -3648,8 +3648,14 @@ Aliases to asynchronous ABCs in :mod:`collections.abc`
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is no ``ReturnType`` type parameter. As with :class:`Generator`, the
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``SendType`` behaves contravariantly.
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If your generator will only yield values, set the ``SendType`` to
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``None``::
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The ``SendType`` defaults to :const:`!None`::
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async def infinite_stream(start: int) -> AsyncGenerator[int]:
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while True:
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yield start
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start = await increment(start)
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It is also possible to set this type explicitly::
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async def infinite_stream(start: int) -> AsyncGenerator[int, None]:
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while True:
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@ -3671,6 +3677,9 @@ Aliases to asynchronous ABCs in :mod:`collections.abc`
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now supports subscripting (``[]``).
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See :pep:`585` and :ref:`types-genericalias`.
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.. versionchanged:: 3.13
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The ``SendType`` parameter now has a default.
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.. class:: AsyncIterable(Generic[T_co])
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Deprecated alias to :class:`collections.abc.AsyncIterable`.
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@ -3754,8 +3763,14 @@ Aliases to other ABCs in :mod:`collections.abc`
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of :class:`Generator` behaves contravariantly, not covariantly or
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invariantly.
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If your generator will only yield values, set the ``SendType`` and
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``ReturnType`` to ``None``::
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The ``SendType`` and ``ReturnType`` parameters default to :const:`!None`::
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def infinite_stream(start: int) -> Generator[int]:
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while True:
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yield start
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start += 1
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It is also possible to set these types explicitly::
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def infinite_stream(start: int) -> Generator[int, None, None]:
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while True:
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@ -3774,6 +3789,9 @@ Aliases to other ABCs in :mod:`collections.abc`
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:class:`collections.abc.Generator` now supports subscripting (``[]``).
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See :pep:`585` and :ref:`types-genericalias`.
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.. versionchanged:: 3.13
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Default values for the send and return types were added.
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.. class:: Hashable
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Deprecated alias to :class:`collections.abc.Hashable`.
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@ -7289,6 +7289,17 @@ class CollectionsAbcTests(BaseTestCase):
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g = foo()
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self.assertIsSubclass(type(g), typing.Generator)
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def test_generator_default(self):
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g1 = typing.Generator[int]
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g2 = typing.Generator[int, None, None]
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self.assertEqual(get_args(g1), (int, type(None), type(None)))
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self.assertEqual(get_args(g1), get_args(g2))
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g3 = typing.Generator[int, float]
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g4 = typing.Generator[int, float, None]
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self.assertEqual(get_args(g3), (int, float, type(None)))
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self.assertEqual(get_args(g3), get_args(g4))
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def test_no_generator_instantiation(self):
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with self.assertRaises(TypeError):
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typing.Generator()
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@ -1328,7 +1328,7 @@ class _BaseGenericAlias(_Final, _root=True):
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raise AttributeError(attr)
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def __setattr__(self, attr, val):
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if _is_dunder(attr) or attr in {'_name', '_inst', '_nparams'}:
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if _is_dunder(attr) or attr in {'_name', '_inst', '_nparams', '_defaults'}:
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super().__setattr__(attr, val)
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else:
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setattr(self.__origin__, attr, val)
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@ -1578,11 +1578,12 @@ class _GenericAlias(_BaseGenericAlias, _root=True):
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# parameters are accepted (needs custom __getitem__).
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class _SpecialGenericAlias(_NotIterable, _BaseGenericAlias, _root=True):
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def __init__(self, origin, nparams, *, inst=True, name=None):
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def __init__(self, origin, nparams, *, inst=True, name=None, defaults=()):
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if name is None:
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name = origin.__name__
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super().__init__(origin, inst=inst, name=name)
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self._nparams = nparams
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self._defaults = defaults
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if origin.__module__ == 'builtins':
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self.__doc__ = f'A generic version of {origin.__qualname__}.'
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else:
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@ -1594,12 +1595,22 @@ class _SpecialGenericAlias(_NotIterable, _BaseGenericAlias, _root=True):
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params = (params,)
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msg = "Parameters to generic types must be types."
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params = tuple(_type_check(p, msg) for p in params)
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if (self._defaults
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and len(params) < self._nparams
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and len(params) + len(self._defaults) >= self._nparams
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):
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params = (*params, *self._defaults[len(params) - self._nparams:])
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actual_len = len(params)
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if actual_len != self._nparams:
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if self._defaults:
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expected = f"at least {self._nparams - len(self._defaults)}"
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else:
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expected = str(self._nparams)
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if not self._nparams:
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raise TypeError(f"{self} is not a generic class")
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raise TypeError(f"Too {'many' if actual_len > self._nparams else 'few'} arguments for {self};"
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f" actual {actual_len}, expected {self._nparams}")
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f" actual {actual_len}, expected {expected}")
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return self.copy_with(params)
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def copy_with(self, params):
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@ -2813,8 +2824,8 @@ DefaultDict = _alias(collections.defaultdict, 2, name='DefaultDict')
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OrderedDict = _alias(collections.OrderedDict, 2)
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Counter = _alias(collections.Counter, 1)
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ChainMap = _alias(collections.ChainMap, 2)
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Generator = _alias(collections.abc.Generator, 3)
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AsyncGenerator = _alias(collections.abc.AsyncGenerator, 2)
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Generator = _alias(collections.abc.Generator, 3, defaults=(types.NoneType, types.NoneType))
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AsyncGenerator = _alias(collections.abc.AsyncGenerator, 2, defaults=(types.NoneType,))
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Type = _alias(type, 1, inst=False, name='Type')
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Type.__doc__ = \
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"""Deprecated alias to builtins.type.
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@ -0,0 +1,2 @@
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Add type parameter defaults to :class:`typing.Generator` and
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:class:`typing.AsyncGenerator`.
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