In order to make an inheritable pipe, the code is quite a bit different between posixes that implement pipe2 and those that don't (osx, mainly). I believe the officially-supported path is to call os.pipe() then os.setinheritable(). This seems objectionable since set_inheritable() code is invoked twice, where I'd prefer to invoke it zero times (or at most once).

Would it be acceptable to implement a pipe2 shim for those platforms?
If so, I'll (attempt to) provide a patch.

Alternatively, can we change the signature of os.pipe() to os.pipe(flags=O_CLOEXEC) ?  In my opinion, such a function could be implemented via pipe2 on those platforms that provide it, obviating any need for an os.pipe2.

Please tell me which patch to provide, if any.

pipe2 can also be used to set O_NONBLOCK, so no, that specific API change wouldn't obsolete pipe2.  So, a shim for pipe2 would be the way to go, since that's currently the de-facto standard way of passing flags on pipe creation in unix land.  (The os module is usually a thin layer over OS services...for other modules we might design a more divergent API, but generally in the os module we do not.)

I notice that dup2 grew an `inheritable=True` argument in 3.4.
This might be a good precedent to use here, as a third option.

> This seems objectionable since set_inheritable() code is invoked
> twice, where I'd prefer to invoke it zero times (or at most once).

Does it make a difference in the grand scheme of things? If you're forking a process, you're usually doing something heavy enough that two calls to set_inheritable() will end up invisible.

os.dup2() is really a special case for inheritable file descriptors. See
the PEP 446.

> Would it be acceptable to implement a pipe2 shim for those platforms?

If I understand correctly, you propose to add an option inheritable parameter to os.pipe():

def os.pipe(inheritable=False):
    ...

The PEP 446 was written to fix race conditions. os.pipe(inheritable=True) would create a race condition if another thread calls fork().

What is your use case? Please elaborate.

The subprocess module makes "pass_fds" file descriptors inheritables in a safe way.

Closing as this seems abandoned.

Buck, if you want to bring it up again and explain the use case, please reopen this issue, create a new issue or post to python-ideas.