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bpo-42236: Use UTF-8 encoding if nl_langinfo(CODESET) fails (GH-23086)

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If the nl_langinfo(CODESET) function returns an empty string, Python
now uses UTF-8 as the filesystem encoding.

In May 2010 (commit b744ba1d14), I
modified Python to log a warning and use UTF-8 as the filesystem
encoding (instead of None) if nl_langinfo(CODESET) returns an empty
string.

In August 2020 (commit 94908bbc15), I
modified Python startup to fail with a fatal error and a specific
error message if nl_langinfo(CODESET) returns an empty string. The
intent was to prevent guessing the encoding and also investigate user
configuration where this case happens.

In 10 years (2010 to 2020), I saw zero user report about the error
message related to nl_langinfo(CODESET) returning an empty string.

Today, UTF-8 became the defacto standard and it's safe to make the
assumption that the user expects UTF-8. For example,
nl_langinfo(CODESET) can return an empty string on macOS if the
LC_CTYPE locale is not supported, and UTF-8 is the default encoding
on macOS.

While this change is likely to not affect anyone in practice, it
should make UTF-8 lover happy ;-)

Rewrite also the documentation explaining how Python selects the
filesystem encoding and error handler.
This commit is contained in:
Victor Stinner 2020-11-01 23:07:23 +01:00 • committed by GitHub
parent 82458b6cdb
commit e662c398d8
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8 changed files with 87 additions and 89 deletions
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35
Include/cpython/initconfig.h
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@ -156,36 +156,13 @@ typedef struct {
/* Python filesystem encoding and error handler:
sys.getfilesystemencoding() and sys.getfilesystemencodeerrors().
Default encoding and error handler:
The Doc/c-api/init_config.rst documentation explains how Python selects
the filesystem encoding and error handler.
* if Py_SetStandardStreamEncoding() has been called: they have the
highest priority;
* PYTHONIOENCODING environment variable;
* The UTF-8 Mode uses UTF-8/surrogateescape;
* If Python forces the usage of the ASCII encoding (ex: C locale
or POSIX locale on FreeBSD or HP-UX), use ASCII/surrogateescape;
* locale encoding: ANSI code page on Windows, UTF-8 on Android and
VxWorks, LC_CTYPE locale encoding on other platforms;
* On Windows, "surrogateescape" error handler;
* "surrogateescape" error handler if the LC_CTYPE locale is "C" or "POSIX";
* "surrogateescape" error handler if the LC_CTYPE locale has been coerced
(PEP 538);
* "strict" error handler.
Supported error handlers: "strict", "surrogateescape" and
"surrogatepass". The surrogatepass error handler is only supported
if Py_DecodeLocale() and Py_EncodeLocale() use directly the UTF-8 codec;
it's only used on Windows.
initfsencoding() updates the encoding to the Python codec name.
For example, "ANSI_X3.4-1968" is replaced with "ascii".
On Windows, sys._enablelegacywindowsfsencoding() sets the
encoding/errors to mbcs/replace at runtime.
See Py_FileSystemDefaultEncoding and Py_FileSystemDefaultEncodeErrors.
*/
_PyUnicode_InitEncodings() updates the encoding name to the Python codec
name. For example, "ANSI_X3.4-1968" is replaced with "ascii". It also
sets Py_FileSystemDefaultEncoding to filesystem_encoding and
sets Py_FileSystemDefaultEncodeErrors to filesystem_errors. */
wchar_t *filesystem_encoding;
wchar_t *filesystem_errors;