1. Need fix the code
2. Fix documentation
3. Update PEP446 description.

There is F_DUPFD_CLOEXEC constant, that must be used instead of F_DUPFD transparently when kernel >= 2.6.24.

I don’t see any violation or anything needing fixing in the documentation or code. Can you elaborate?

The fcntl() documentation says “The values used for ‘cmd’ [F_DUPFD, etc] are operating system dependent, and are available as constants in the ‘fcntl’ module, using the same names as used in the relevant C header files.” The newest version of Posix specifies both the F_DUPFD and F_DUPFD_CLOEXEC. It would be misleading for Python to use one when the user specified the other.

If you want a best-effort version of F_DUPFD_CLOEXEC for a single-threaded program, why not use os.dup()? I presume this uses F_DUPFD_CLOEXEC where appropriate, and uses some non-atomic fallback if necessary.

I don't think that it's possible nor worth it to wrap all fcntl() and all
ioctl() calls. I see these functions as very low-level APIs and so I
consider that the caller is responsible of what he/she does.

If you want to change something, explian in fcntl module doc that the PEP
466 is not implemented in this module znd it's a deliberate choice.

I agree with Martin, it's the responsability of the dev to use the right
command depending on the use case.

OK, it will be consistent, if docs mention that F_DUPFD will not set O_CLOEXEC automatically, mentiont that F_DUPFD_CLOEXEC should be used for that, and also mention PEP446 somewhere.