STINNER Victor wrote:
> 
> STINNER Victor <victor.stinner@haypocalc.com> added the comment:
> 
>> I think that using ASCII is a safer choice in case of errors.
> 
> I choosed UTF-8 to keep backward compatibility: PyUnicode_DecodeFSDefaultAndSize() uses utf-8 if Py_FileSystemDefaultEncoding==NULL. If the OS has no nl_langinfo(CODESET) function at all, Python3 uses utf-8.

Ouch, that was a poor choice. In Python we have a tradition to
avoid guessing, if possible. Since we cannot guarantee that the
file system will indeed use UTF-8, it would have been safer to
use ASCII. Not sure why this reasoning wasn't applied for
the file system encoding.

Nothing we can do about now, though.

>> Using UTF-8 may be safe for reading file names, but it's not
>> safe for creating files or directories.
> 
> Well, I don't know. You are maybe right. And which encoding should be used if nl_langinfo(CODESET) function is missing: ASCII or UTF-8?
> 
> UTF-8 is also an optimist choice: I bet that more and more OS will move to UTF-8.

I think we should also add a new environment variable to override
the automatic determination of the file system encoding, much like
what we have for the I/O encoding:

PYTHONFSENCODING: Encoding[:errors] used for file system.

(that would need to go on a new ticket, though)