[Python-Dev] Best Python API for exposing posix_spawn

[Brett Cannon]

On Tue, 9 Jan 2018 at 02:42 Nick Coghlan <ncoghlan at gmail.com> wrote:

> On 9 January 2018 at 20:01, Antoine Pitrou <solipsis at pitrou.net> wrote:
> > On Mon, 08 Jan 2018 09:11:38 +0000
> > Pablo Galindo Salgado <pablogsal at gmail.com> wrote:
> >> Hi,
> >>
> >> I'm currently working on exposing posix_spawn in the posix module (and
> by
> >> extension in the os module). You can find the initial implementation in
> >> this PR:
> >>
> >> https://github.com/python/cpython/pull/5109
> >>
> >> As pointed out by Gregory P. Smith, some changes are needed in the way
> the
> >> file_actions arguments is passed from Python. For context, posix_spawn
> has
> >> the following declaration:
> >>
> >> int posix_spawn(pid_t *pid, const char *path,
> >> const posix_spawn_file_actions_t *file_actions,
> >> const posix_spawnattr_t *attrp,
> >> char *const argv[], char *const envp[]);
> >>
> >> Here, file_actions is an object that represents a list of file actions
> >> (open, close or dup2) that is populated using helper functions on the C
> API.
> >>
> >> The question is: what is the best way to deal with this argument?
> >
> > How about a list of tuples like:
> > [(os.SPAWN_OPEN, 4, 'README.txt', os.O_RDONLY, 0),
> >  (os.SPAWN_CLOSE, 5),
> >  (os.SPAWN_DUP2, 3, 6),
> >  ]
> >
> > I don't expect this API to be invoked directly by user code so it
> > doesn't have to be extremely pretty.
>
> I'll note that one advantage of this approach is that it ties in well
> with how the C API is going to have to deal with it anyway: a switch
> statement dispatching on the first value, and then passing the
> remaining arguments to the corresponding posix_file_actions API.
>

Plus the posix module tends to stick reasonably close to the C API anyway
since it's such a thin wrapper.


>
> Wrapping it all up in a more Pythonic self-validating API would then
> be the responsibility of the subprocess module (in the standard
> library), or third party modules.
>

+1 from me on Antoine's suggestion. Might as well keep it simple.
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