API to execute code in child process before execv?

[pexpect]

API to execute code in child process before execv?

[jquast]

Agreed for this. More documentation than code: we need to be clear to be very careful not to raise any exceptions, as they cannot be caught or handled.

[takluyver]

I added this already to ptyprocess:
https://github.com/pexpect/ptyprocess/blob/master/ptyprocess/ptyprocess.py#L170

It takes an iterable of functions to be called with no arguments, and currently does no error handling. I'd appreciate a review of this design before moving forwards with it. I found since writing that that subprocess.Popen() has a preexec_fn parameter which takes a single callable, and calls it from C code (on POSIX only). There, errors are handled with the same pipe approach used for exec failure. We also have that ability (pexpect/ptyprocess#1), and I think we should use it for this.

Do you see any reasons to prefer either an iterable of functions, as I currently have, or a single function, like subprocess uses? I'm leaning slightly towards a single function for consistency with the stdlib; that function can always call other functions if the user really needs that.

[jquast]

I'd go with the single function and consistency of naming the argument preexec_fn as well.

There's no reason an implementer can't have their target chain multiple functions, good find on the preexec_fn.

[takluyver]

I made a start on this in pexpect/ptyprocess#6.

[jquast]

Closing, keyword argument preexec_fn of spawn() satisfies this issue.