open() documentation still says default encoding is locale-dependent in 3.15

[honglei]

Documentation

Documentation page

https://docs.python.org/3.15/library/functions.html#open

Bug description

The Python 3.15 open() documentation still says that the default encoding is platform-dependent and comes from locale.getencoding().

But What's New in Python 3.15 says that Python 3.15 now uses UTF-8 as the default encoding for text files by default (PEP 686), independent of the system locale/environment:
https://docs.python.org/3.15/whatsnew/3.15.html#whatsnew315-utf8-default

So these pages appear inconsistent and the open() docs may still have pre-3.15 wording.

Linked PRs

• gh-148603: Update open() default encoding docs #148614

[vstinner]

open() now uses the UTF-8 encoding by default, but it still uses the locale encoding if the UTF-8 Mode is disabled:

$ LANG=fr_FR python3.15 -c 'print(open("/etc/issue").encoding)'
utf-8
$ LANG=fr_FR python3.15 -X utf8=0 -c 'print(open("/etc/issue").encoding)'
ISO-8859-1

[dagangtj]

I would like to work on this documentation fix and will open a PR shortly.