Fix accepted types in select.select

[sobolevn]

No errors happen in type checking time for select(['a'], ['b'], ['c']). See https://mypy-play.net/?gist=2a5c9fcecebd7dbfd6f9823f605da0e5

Not any values are allowed in select.select. It only allows int | HasFileno items. See:

>>> from select import select
... 
... select(['a', 'b'], [], [])
... 
Traceback (most recent call last):
  File "<python-input-0>", line 3, in <module>
    select(['a', 'b'], [], [])
    ~~~~~~^^^^^^^^^^^^^^^^^^^^
TypeError: argument must be an int, or have a fileno() method.
>>> 
KeyboardInterrupt
>>> 
                                                                                           
(.venv) ~/Desktop/cpython  issue-149609 ✔                                                 
» python  
Python 3.14.2 (main, Mar 16 2026, 20:11:03) [Clang 17.0.0 (clang-1700.6.3.2)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from select import select
... 
... select(['a'], [], [])
... 
Traceback (most recent call last):
  File "<python-input-2>", line 3, in <module>
    select(['a'], [], [])
    ~~~~~~^^^^^^^^^^^^^^^
TypeError: argument must be an int, or have a fileno() method.
>>> from select import select
... 
... select([], ['a'], [])
... 
Traceback (most recent call last):
  File "<python-input-0>", line 3, in <module>
    select([], ['a'], [])
    ~~~~~~^^^^^^^^^^^^^^^
TypeError: argument must be an int, or have a fileno() method.
>>> from select import select
... 
... select([], [], ['a'])
... 
Traceback (most recent call last):
  File "<python-input-1>", line 3, in <module>
    select([], [], ['a'])
    ~~~~~~^^^^^^^^^^^^^^^
TypeError: argument must be an int, or have a fileno() method.

Why is that?

1. All passed lists are passed to seq2set: https://github.com/python/cpython/blob/53c3dd9a8d79a331764147b7b7b01f9d0a8bce71/Modules/selectmodule.c#L344-L349
2. seq2set calls PyObject_AsFileDescriptor on list items https://github.com/python/cpython/blob/53c3dd9a8d79a331764147b7b7b01f9d0a8bce71/Modules/selectmodule.c#L168
3. It requires int or HasFileno type: https://github.com/python/cpython/blob/53c3dd9a8d79a331764147b7b7b01f9d0a8bce71/Objects/fileobject.c#L172-L182

[sobolevn]

• https://github.com/apache/spark/blob/1659122ca40126e7efc17a550850974bb2022762/python/pyspark/daemon.py#L193 here mypy does not handle list inference well, because it joins a _IOBase type with int and gets object, this is not related to the annotation itself.
• https://github.com/canonical/operator/blob/f4026b577536b56b54afecace7bbde174f438262/ops/pebble.py#L1902 here mypy does not handle list inference well, because it joins a _IOBase type with int and gets object, this is not related to the annotation itself.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

spark (https://github.com/apache/spark)
+ python/pyspark/daemon.py:193: error: Value of type variable "_R" of "select" cannot be "object"  [type-var]

operator (https://github.com/canonical/operator)
+ ops/pebble.py:1902: error: Value of type variable "_R" of "select" cannot be "object"  [type-var]