Having slept on it and given the extra info you've provided I'm more comfortable with the proposed solution now. :)

So the result will be that on 32-bit architectures only 32-bit (signed) ints will be allowed through channels.  On 64-bit platforms (and higher) it will still be 64-bit ints.  That's a livable outcome, particularly since 32-bit platforms already have to deal with such variation already. :)  Plus, the consistency with sys.maxsize makes sense.

The alternative (on 32-bit arch) would be to send through a struct containing the long long, similar to what we do for str and bytes.  I don't think that's worth it.  If it matters we can do something like that later (since it's an implementation detail).

Consequently, I've approved the PR.  I'll merge it in a little while.

Thanks for working on this.