Add versionadded for typing.Generator defaults

[ivanovkirilg]

In a project requiring Python >= 3.12, I was baffled by the following error:

TypeError: Too few arguments for typing.Generator; actual 1, expected 3

especially when reading the docs for typing.Generator, which claimed that one argument is sufficient.

The SendType and ReturnType parameters default to None:
...

That is until I went to the 3.12 docs which state that one must

set the SendType and ReturnType to None:
...

---

Hence I propose a versionadded note.
I looked around the page for examples and determined that a plain versionadded tag without the note may look like it applies to the entire Generator.

However, the way I've worded it seems a bit verbose; feedback is welcome.

Result

I built the docs locally, this is what the note looks like in context:

---

I'm not sure if this change leans towards 'typo' or requiring an issue, so I went down the "path of least resistance" 🙂

If this is accepted, I intend to backport it to the 3.13–3.15 docs.

[python-cla-bot]

All commit authors signed the Contributor License Agreement.

[picnixz]

If this is accepted, I intend to backport it to the 3.13–3.15 docs.

It's unfortunate but 3.13 is sec-only so it doesn't accept such PRs. But we can backport it to 3.14-3.15.

[picnixz]

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]

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]

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]

Wait: typing.Generator does exist and contains:

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