[Python-ideas] Tulip / PEP 3156 - subprocess events

[Eli Bendersky]

On Sun, Jan 20, 2013 at 3:25 PM, Paul Moore <p.f.moore at gmail.com> wrote:

> On 20 January 2013 22:53, Andrew Bennetts <andrew at bemusement.org> wrote:
> > Guido van Rossum wrote:
> > […]
> >> I have a more-or-less working but probably incomplete version checked
> >> into the tulip repo:
> >>
> http://code.google.com/p/tulip/source/browse/tulip/subprocess_transport.py
> >>
> >> Note that this completely ignores stderr -- this makes the code
> >> simpler while still useful (there's plenty of useful stuff you can do
> >> without reading stderr), and avoids the questions Greg Ewing brought
> >> up about needing two transports (one for stdout, another for stderr).
> >
> > Although 3 pipes to a subprocess (stdin, stdout, stderr) is the usual
> > convention, it's not the only possibility, so that configuration
> > shouldn't be hard-coded.  On POSIX some programs can and do make use of
> > the ability to have more pipes to a subprocess; e.g. the various *fd
> > options of gnupg (--status-fd, --logger-fd, --command-fd, and so on).
> > And some programs give the child process file descriptors that aren't
> > pipes, like sockets (e.g. an inetd-like server that accepts a socket
> > then spawns a subprocess to serve it).
> >
> > So I hope tulip will support these possibilities (although obviously the
> > stdin/out/err style should be the convenient default).  You will be
> > unsurprised to hear that Twisted does :)
>
> My plan is to modify Guido's current code to take a subprocess.Popen
> object when creating a connection to a subprocess. So you'd use the
> existing API to start the process, and then tulip to interact with it.
> Having said that, I have no idea if or how subprocess.Popen would
> support the extra fds you are talking about. If you can show me some
> sample code, I can see what would be needed to handle it. But as far
> as I know, subprocess.Popen objects only have the 3 standard handles
> exposed as attributes - stdin, stdout and stderr.
>
>
subprocess.Popen has the pass_fds argument, documented as follows:

    *pass_fds* is an optional sequence of file descriptors to keep open
between the parent and child. Providing any *pass_fds* forces *close_fds*to be
True <http://docs.python.org/dev/library/constants.html#True>. (Unix only)

Eli
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