gh-123523: Rework typing documentation for generators and coroutines, and link to it from collections.abc docs (#123544)

Author: sterliakov

Doc/library/collections.abc.rst

@@ -213,6 +213,9 @@ Collections Abstract Base Classes -- Detailed Descriptions
 
    ABC for classes that provide the :meth:`~object.__call__` method.
 
+   See :ref:`annotating-callables` for details on how to use
+   :class:`!Callable` in type annotations.
+
 .. class:: Iterable
 
    ABC for classes that provide the :meth:`~container.__iter__` method.
@@ -250,6 +253,9 @@ Collections Abstract Base Classes -- Detailed Descriptions
    :meth:`~generator.send`,
    :meth:`~generator.throw` and :meth:`~generator.close` methods.
 
+   See :ref:`annotating-generators-and-coroutines`
+   for details on using :class:`!Generator` in type annotations.
+
    .. versionadded:: 3.5
 
 .. class:: Sequence
@@ -321,6 +327,11 @@ Collections Abstract Base Classes -- Detailed Descriptions
       Using ``isinstance(gencoro, Coroutine)`` for them will return ``False``.
       Use :func:`inspect.isawaitable` to detect them.
 
+   See :ref:`annotating-generators-and-coroutines`
+   for details on using :class:`!Coroutine` in type annotations.
+   The variance and order of type parameters correspond to those of
+   :class:`Generator`.
+
    .. versionadded:: 3.5
 
 .. class:: AsyncIterable
@@ -342,6 +353,9 @@ Collections Abstract Base Classes -- Detailed Descriptions
    ABC for :term:`asynchronous generator` classes that implement the protocol
    defined in :pep:`525` and :pep:`492`.
 
+   See :ref:`annotating-generators-and-coroutines`
+   for details on using :class:`!AsyncGenerator` in type annotations.
+
    .. versionadded:: 3.6
 
 .. class:: Buffer

Doc/library/typing.rst

@@ -208,7 +208,7 @@ Annotating callable objects
 ===========================
 
 Functions -- or other :term:`callable` objects -- can be annotated using
-:class:`collections.abc.Callable` or :data:`typing.Callable`.
+:class:`collections.abc.Callable` or deprecated :data:`typing.Callable`.
 ``Callable[[int], str]`` signifies a function that takes a single parameter
 of type :class:`int` and returns a :class:`str`.
 
@@ -401,7 +401,7 @@ The type of class objects
 =========================
 
 A variable annotated with ``C`` may accept a value of type ``C``. In
-contrast, a variable annotated with ``type[C]`` (or
+contrast, a variable annotated with ``type[C]`` (or deprecated
 :class:`typing.Type[C] <Type>`) may accept values that are classes
 themselves -- specifically, it will accept the *class object* of ``C``. For
 example::
@@ -441,6 +441,87 @@ For example::
 ``type[Any]`` is equivalent to :class:`type`, which is the root of Python's
 :ref:`metaclass hierarchy <metaclasses>`.
 
+
+.. _annotating-generators-and-coroutines:
+
+Annotating generators and coroutines
+====================================
+
+A generator can be annotated using the generic type
+:class:`Generator[YieldType, SendType, ReturnType] <collections.abc.Generator>`.
+For example::
+
+   def echo_round() -> Generator[int, float, str]:
+       sent = yield 0
+       while sent >= 0:
+           sent = yield round(sent)
+       return 'Done'
+
+Note that unlike many other generic classes in the standard library,
+the ``SendType`` of :class:`~collections.abc.Generator` behaves
+contravariantly, not covariantly or invariantly.
+
+The ``SendType`` and ``ReturnType`` parameters default to :const:`!None`::
+
+   def infinite_stream(start: int) -> Generator[int]:
+       while True:
+           yield start
+           start += 1
+
+It is also possible to set these types explicitly::
+
+   def infinite_stream(start: int) -> Generator[int, None, None]:
+       while True:
+           yield start
+           start += 1
+
+Simple generators that only ever yield values can also be annotated
+as having a return type of either
+:class:`Iterable[YieldType] <collections.abc.Iterable>`
+or :class:`Iterator[YieldType] <collections.abc.Iterator>`::
+
+   def infinite_stream(start: int) -> Iterator[int]:
+       while True:
+           yield start
+           start += 1
+
+Async generators are handled in a similar fashion, but don't
+expect a ``ReturnType`` type argument
+(:class:`AsyncGenerator[YieldType, SendType] <collections.abc.AsyncGenerator>`).
+The ``SendType`` argument defaults to :const:`!None`, so the following definitions
+are equivalent::
+
+   async def infinite_stream(start: int) -> AsyncGenerator[int]:
+       while True:
+           yield start
+           start = await increment(start)
+
+   async def infinite_stream(start: int) -> AsyncGenerator[int, None]:
+       while True:
+           yield start
+           start = await increment(start)
+
+As in the synchronous case,
+:class:`AsyncIterable[YieldType] <collections.abc.AsyncIterable>`
+and :class:`AsyncIterator[YieldType] <collections.abc.AsyncIterator>` are
+available as well::
+
+   async def infinite_stream(start: int) -> AsyncIterator[int]:
+       while True:
+           yield start
+           start = await increment(start)
+
+Coroutines can be annotated using
+:class:`Coroutine[YieldType, SendType, ReturnType] <collections.abc.Coroutine>`.
+Generic arguments correspond to those of :class:`~collections.abc.Generator`,
+for example::
+
+   from collections.abc import Coroutine
+   c: Coroutine[list[str], str, int]  # Some coroutine defined elsewhere
+   x = c.send('hi')                   # Inferred type of 'x' is list[str]
+   async def bar() -> None:
+       y = await c                    # Inferred type of 'y' is int
+
 .. _user-defined-generics:
 
 User-defined generic types
@@ -3318,14 +3399,9 @@ Aliases to built-in types
    Deprecated alias to :class:`dict`.
 
    Note that to annotate arguments, it is preferred
-   to use an abstract collection type such as :class:`Mapping`
+   to use an abstract collection type such as :class:`~collections.abc.Mapping`
    rather than to use :class:`dict` or :class:`!typing.Dict`.
 
-   This type can be used as follows::
-
-      def count_words(text: str) -> Dict[str, int]:
-          ...
-
    .. deprecated:: 3.9
       :class:`builtins.dict <dict>` now supports subscripting (``[]``).
       See :pep:`585` and :ref:`types-genericalias`.
@@ -3335,16 +3411,9 @@ Aliases to built-in types
    Deprecated alias to :class:`list`.
 
    Note that to annotate arguments, it is preferred
-   to use an abstract collection type such as :class:`Sequence` or
-   :class:`Iterable` rather than to use :class:`list` or :class:`!typing.List`.
-
-   This type may be used as follows::
-
-      def vec2[T: (int, float)](x: T, y: T) -> List[T]:
-          return [x, y]
-
-      def keep_positives[T: (int, float)](vector: Sequence[T]) -> List[T]:
-          return [item for item in vector if item > 0]
+   to use an abstract collection type such as
+   :class:`~collections.abc.Sequence` or :class:`~collections.abc.Iterable`
+   rather than to use :class:`list` or :class:`!typing.List`.
 
    .. deprecated:: 3.9
       :class:`builtins.list <list>` now supports subscripting (``[]``).
@@ -3355,8 +3424,8 @@ Aliases to built-in types
    Deprecated alias to :class:`builtins.set <set>`.
 
    Note that to annotate arguments, it is preferred
-   to use an abstract collection type such as :class:`AbstractSet`
-   rather than to use :class:`set` or :class:`!typing.Set`.
+   to use an abstract collection type such as :class:`collections.abc.Set`
+   rather than to use :class:`set` or :class:`typing.Set`.
 
    .. deprecated:: 3.9
       :class:`builtins.set <set>` now supports subscripting (``[]``).
@@ -3544,11 +3613,6 @@ Aliases to container ABCs in :mod:`collections.abc`
 
    Deprecated alias to :class:`collections.abc.Mapping`.
 
-   This type can be used as follows::
-
-      def get_position_in_index(word_list: Mapping[str, int], word: str) -> int:
-          return word_list[word]
-
    .. deprecated:: 3.9
       :class:`collections.abc.Mapping` now supports subscripting (``[]``).
       See :pep:`585` and :ref:`types-genericalias`.
@@ -3612,14 +3676,9 @@ Aliases to asynchronous ABCs in :mod:`collections.abc`
 
    Deprecated alias to :class:`collections.abc.Coroutine`.
 
-   The variance and order of type variables
-   correspond to those of :class:`Generator`, for example::
-
-      from collections.abc import Coroutine
-      c: Coroutine[list[str], str, int]  # Some coroutine defined elsewhere
-      x = c.send('hi')                   # Inferred type of 'x' is list[str]
-      async def bar() -> None:
-          y = await c                    # Inferred type of 'y' is int
+   See :ref:`annotating-generators-and-coroutines`
+   for details on using :class:`collections.abc.Coroutine`
+   and ``typing.Coroutine`` in type annotations.
 
    .. versionadded:: 3.5.3
 
@@ -3631,40 +3690,9 @@ Aliases to asynchronous ABCs in :mod:`collections.abc`
 
    Deprecated alias to :class:`collections.abc.AsyncGenerator`.
 
-   An async generator can be annotated by the generic type
-   ``AsyncGenerator[YieldType, SendType]``. For example::
-
-      async def echo_round() -> AsyncGenerator[int, float]:
-          sent = yield 0
-          while sent >= 0.0:
-              rounded = await round(sent)
-              sent = yield rounded
-
-   Unlike normal generators, async generators cannot return a value, so there
-   is no ``ReturnType`` type parameter. As with :class:`Generator`, the
-   ``SendType`` behaves contravariantly.
-
-   The ``SendType`` defaults to :const:`!None`::
-
-      async def infinite_stream(start: int) -> AsyncGenerator[int]:
-          while True:
-              yield start
-              start = await increment(start)
-
-   It is also possible to set this type explicitly::
-
-      async def infinite_stream(start: int) -> AsyncGenerator[int, None]:
-          while True:
-              yield start
-              start = await increment(start)
-
-   Alternatively, annotate your generator as having a return type of
-   either ``AsyncIterable[YieldType]`` or ``AsyncIterator[YieldType]``::
-
-      async def infinite_stream(start: int) -> AsyncIterator[int]:
-          while True:
-              yield start
-              start = await increment(start)
+   See :ref:`annotating-generators-and-coroutines`
+   for details on using :class:`collections.abc.AsyncGenerator`
+   and ``typing.AsyncGenerator`` in type annotations.
 
    .. versionadded:: 3.6.1
 
@@ -3746,40 +3774,9 @@ Aliases to other ABCs in :mod:`collections.abc`
 
    Deprecated alias to :class:`collections.abc.Generator`.
 
-   A generator can be annotated by the generic type
-   ``Generator[YieldType, SendType, ReturnType]``. For example::
-
-      def echo_round() -> Generator[int, float, str]:
-          sent = yield 0
-          while sent >= 0:
-              sent = yield round(sent)
-          return 'Done'
-
-   Note that unlike many other generics in the typing module, the ``SendType``
-   of :class:`Generator` behaves contravariantly, not covariantly or
-   invariantly.
-
-   The ``SendType`` and ``ReturnType`` parameters default to :const:`!None`::
-
-      def infinite_stream(start: int) -> Generator[int]:
-          while True:
-              yield start
-              start += 1
-
-   It is also possible to set these types explicitly::
-
-      def infinite_stream(start: int) -> Generator[int, None, None]:
-          while True:
-              yield start
-              start += 1
-
-   Alternatively, annotate your generator as having a return type of
-   either ``Iterable[YieldType]`` or ``Iterator[YieldType]``::
-
-      def infinite_stream(start: int) -> Iterator[int]:
-          while True:
-              yield start
-              start += 1
+   See :ref:`annotating-generators-and-coroutines`
+   for details on using :class:`collections.abc.Generator`
+   and ``typing.Generator`` in type annotations.
 
    .. deprecated:: 3.9
       :class:`collections.abc.Generator` now supports subscripting (``[]``).