Eryk Sun <eryk...@gmail.com> added the comment:
> # Power Shell 6 (use cp65001 by default)
> PS C:¥> python3 -c "print('おはよう')" > ps.txt
PowerShell standard I/O redirection is different from any shell I've ever used.
In this case, it runs Python with StandardOutput set to a handle for a pipe
instead of a handle for the file. It decodes Python's output using whatever
encoding is configured for input and re-encodes it with whatever encoding is
configured for output.
To see what Python is actually writing, try using Start-Process with
StandardOutput redirected to the file. For example:
Start-Process -FilePath python3.exe -ArgumentList "-c `"print('おはよう')`""
-NoNewWindow -Wait -RedirectStandardOutput ps.txt
> # cmd.exe
> C:¥> chcp 65001
> C:¥> python3 -c "print('おはよう')" > cmd.txt
CMD uses simple redirection, like every other shell I've ever used. It runs
python3.exe with a handle for the file as its StandardOutput. So "cmd.txt"
contains exactly what Python writes.
> * TextIOWrapper tries `os.device_encoding(1)`
> * `os.device_encoding(1)` use GetConsoleOutputCP() without checking stdout is
> console
No, _Py_device_encoding returns None if the isatty(fd) is false, i.e. for a
pipe or disk file. In this case, TextIOWrapper defaults to the encoding from
locale.getpreferredencoding().
The current preferred encoding is the system ANSI codepage from GetACP().
Changing the default to UTF-8 would be disruptive. You can use UTF-8 mode (i.e.
-X utf8). Or, to override just stdin, stdout, and stderr, set the environment
variable "PYTHONIOENCODING=utf-8".
> In the example above, a console is attached when python is called from
> Power Shell 6, but it is not attached when python is called from
> cmd.exe.
In both cases the Python process inherits the console of the parent shell. The
only way to run python.exe without a console is to use the CreateProcess
creation flag DETACHED_PROCESS.
> There is a relating issue: UTF-8 mode doesn't override
> stdin,stdout,stderr encoding when console is attached.
It works for me. For example, testing with stdout redirected to a pipe:
C:\>python -c "import sys;print(sys.stdout.encoding)" | more
cp1252
C:\>python -X utf8 -c "import sys;print(sys.stdout.encoding)" | more
utf-8
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<https://bugs.python.org/issue37275>
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