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Add versionadded for typing.Generator defaults #158967

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4 changes: 4 additions & 0 deletions Doc/library/typing.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -473,6 +473,10 @@ The ``SendType`` and ``ReturnType`` parameters default to :const:`!None`::
yield start
start += 1

.. versionadded:: 3.13

Comment on lines +476 to +477

@picnixz picnixz Oct 7, 2026

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We usually use versionadded when we add a new top-level object / function / module / method and versionchanged otherwise when we change something that already exists.

In addition, we put the version* changes at the end of the section for the object. As such, I would suggest that you change the entry of collections.abc.Generator instead of here.

@AlexWaygood AlexWaygood Oct 7, 2026

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The docs update can't go on collections.abc.Generator because collections.abc.Generator has never validated the number of arguments passed as strictly as typing.Generator. It's always been allowed at runtime to pass only a single argument to collections.abc.Generator. On Python 3.12:

% uvx python3.12
Python 3.12.13 (main, May 10 2026, 19:20:41) [Clang 22.1.3 ] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import typing, collections.abc
>>> typing.Generator[int]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/alexwaygood/.local/share/uv/python/cpython-3.12.13-macos-aarch64-none/lib/python3.12/typing.py", line 398, in inner
    return func(*args, **kwds)
           ^^^^^^^^^^^^^^^^^^^
  File "/Users/alexwaygood/.local/share/uv/python/cpython-3.12.13-macos-aarch64-none/lib/python3.12/typing.py", line 1482, in __getitem__
    _check_generic(self, params, self._nparams)
  File "/Users/alexwaygood/.local/share/uv/python/cpython-3.12.13-macos-aarch64-none/lib/python3.12/typing.py", line 304, in _check_generic
    raise TypeError(f"Too {'many' if alen > elen else 'few'} arguments for {cls};"
TypeError: Too few arguments for typing.Generator; actual 1, expected 3
>>> collections.abc.Generator[int]
collections.abc.Generator[int]
>>>

@picnixz picnixz Oct 7, 2026

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Oh. Mmmh, but it's weird then that this is in middle of a prose paragraph where we link to collections.abc.Generator and not typing.Generator.

@picnixz picnixz Oct 7, 2026

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Wait: typing.Generator does exist and contains:

   .. versionchanged:: 3.13
      Default values for the send and return types were added.

Added default :const:`!None` for ``SendType`` and ``ReturnType``

It is also possible to set these types explicitly::

def infinite_stream(start: int) -> Generator[int, None, None]:
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