bpo-43510: Implement PEP 597 opt-in EncodingWarning. (GH-19481)
See [PEP 597](https://www.python.org/dev/peps/pep-0597/).
* Add `-X warn_default_encoding` and `PYTHONWARNDEFAULTENCODING`.
* Add EncodingWarning
* Add io.text_encoding()
* open(), TextIOWrapper() emits EncodingWarning when encoding is omitted and warn_default_encoding is enabled.
* _pyio.TextIOWrapper() uses UTF-8 as fallback default encoding used when failed to import locale module. (used during building Python)
* bz2, configparser, gzip, lzma, pathlib, tempfile modules use io.text_encoding().
* What's new entry
diff --git a/Doc/c-api/init_config.rst b/Doc/c-api/init_config.rst
index db7c1f4..29fbb68 100644
--- a/Doc/c-api/init_config.rst
+++ b/Doc/c-api/init_config.rst
@@ -583,6 +583,15 @@
Default: ``0``.
+ .. c:member:: int warn_default_encoding
+
+ If non-zero, emit a :exc:`EncodingWarning` warning when :class:`io.TextIOWrapper`
+ uses its default encoding. See :ref:`io-encoding-warning` for details.
+
+ Default: ``0``.
+
+ .. versionadded:: 3.10
+
.. c:member:: wchar_t* check_hash_pycs_mode
Control the validation behavior of hash-based ``.pyc`` files: