> > only one Popen instance (for the iconv call), but different encodings
> > for stdin and stdout.
> Isn't that the exception rather than the rule? I think it actually makes
> sense, in at least 99.83% of cases ;-), to have a common encoding
> setting for all streams.

FWIW, I recently encountered a scenario (albeit in a test situation) where the ability to set different encodings for stdout and stderr would have been useful to me.  It was while creating a test case for issue 15595.  I was changing the locale encoding for stdout, but I also wanted to leave it unchanged for stderr because there didn't seem to be a way to control the encoding that the child used for stderr.