Question about propagating universal_newlines through subprocess.Popen to io.TextIOWrapper

[eryk sun]

On Mon, Jun 26, 2017 at 5:23 PM, Bill Deegan <bill at baddogconsulting.com> wrote:
>
> That universal_newlines value is discarded due to:
>
> text_mode = encoding or errors or universal_newlines
>
> ...
>
> if text_mode:
>     self.stdout = io.TextIOWrapper(self.stdout,
>             encoding=encoding, errors=errors)
>
> There doesn't seem to be a way to set encoding without forcing
> univeral_newlines.
>
> This seems like a bug?

The behavior is documented:

    If encoding or errors are specified, or universal_newlines is true,
    the file objects stdin, stdout and stderr will be opened in text
    mode using the encoding and errors specified in the call or the
    defaults for io.TextIOWrapper.

    For stdin, line ending characters '\n' in the input will be
    converted to the default line separator os.linesep. For stdout and
    stderr, all line endings in the output will be converted to '\n'.
    For more information see the documentation of the io.TextIOWrapper
    class when the newline argument to its constructor is None.

Prior to 3.6, the way to get text streams was to enable
universal_newlines. Maybe for 3.7 the default can change to None, with
the addition of the following code:

    if universal_newlines is None or universal_newlines:
        newline = None
    else:
        newline = ''

    if text_mode:
        self.stdin = io.TextIOWrapper(self.stdin, write_through=True,
                line_buffering=(bufsize == 1),
                encoding=encoding, errors=errors, newline=newline)