[Python-Dev] Implementing File Modes

[Steven D'Aprano]

On Tue, 28 Jul 2009 04:06:45 am Eric Pruitt wrote:
> I am implementing the file wrapper using changes to subprocess.Popen
> that also make it asynchronous and non-blocking so implementing "r+"
> should be trivial to do. How about handling stderr? I have the
> following ideas: leave out support for reading from stderr, make it
> so that there is an optional additional argument like "outputstderr =
> False", create another function that toggles / sets whether stderr or
> stdout is returned or mix the two outputs.

Leaving it out is always an option.

As I see it, fundamentally you can either read from stdout and sterr as 
two different streams, or you can interleave (mix) them. To me, that 
suggests three functions:

ProcessIOWrapper()  # read from stdout (or write to stdin etc.)
ProcessIOWrapperStdErr()  # read/write from stderr
ProcessIOWrapper2()  # read from mixed stdout and stderr

I don't like a function to toggle between one and the other: that smacks 
of relying on a global setting in a bad way. I suppose you could add an 
optional argument to ProcessIOWrapper() to select between stdout, 
stderr, or both together.



-- 
Steven D'Aprano