[Python-Dev] Best Python API for exposing posix_spawn (original) (raw)

Nick Coghlan ncoghlan at gmail.com
Tue Jan 9 05:41:48 EST 2018

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 posixspawn 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 fileactions arguments is passed from Python. For context, posixspawn has the following declaration: int posixspawn(pidt *pid, const char *path, const posixspawnfileactionst *fileactions, const posixspawnattrt *attrp, char *const argv[], char *const envp[]); Here, fileactions 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.SPAWNOPEN, 4, 'README.txt', os.ORDONLY, 0), (os.SPAWNCLOSE, 5), (os.SPAWNDUP2, 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.

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.

Cheers, Nick.

-- Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia

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