From current `os` documentation:

> A file descriptor has an “inheritable” flag which indicates if the file descriptor can be inherited by child processes

from current `subprocess` documentation:

> If close_fds is true, all file descriptors except 0, 1 and 2 will be closed before the child process is executed

It would be helpful to explicitly specify that subprocess.Popen does not takes into account the inheritable flag ; thas is, that inheritable fds will still be closed with open_fds = False, and that non-inheritable fds will still be kept with open_fds = True.

There is no “open_fds” parameter as far as I know. I presume you meant heritable descriptors are still closed with close_fds=True (not open_fds=False).

Are you sure about the second part? In my experiments on Linux, unless I use “pass_fds” or one of the “stdin” etc parameters, a non-heritable descriptor is never passed to the child, no matter what I use for “close_fds”.

Reading through Issue 6559, the intention of “pass_fds” seems to be to list extra file descriptors, in addition to 0, 1 and 2 that are normally passed. The documentation says descriptors greater than 2 are closed (due to close_fds=True), but in reality the “pass_fds” descriptors seem to be always left open, even when they are marked non-heritable.

I assumed simon meant "close_fds=False" when he wrote open_fds = True.

Regardless, supplying any pass_fds forces close_fds=True behavior.

File descriptors listed in pass_fds are explicitly set inheritable from within the child process prior to calling exec().  See the start of child_exec() within Modules/_posixsubprocess.c.

I clarified the docs to mention that the inheritable flag is heeded when close_fds=False in https://github.com/python/cpython/pull/6240/files