Teleport functions' keyword-only argument defaults

[Jongy]

Adds support for teleportation of function defaults of the type def f(*, b=5) (keyword-only argument defaults)

Note that the new code I included is not Python 2 compatible. I thought it's okay to do saw because I noticed you have dropped Python 2 support (7afaec2).

Also - this breaks teleportation compatibility across different RPyC versions. Is this a feature we try to maintain? If so, I can see how to add such support.

[Jongy]

Ran teleportation tests on Python 3.6, 3.8

[comrumino]

Everything looks pretty good. I'll probably make some minor changes like reducing some accidental complexity I found---funcobj.__kwdefaults__ = {t[0]: t[1] for t in kwdefaults} could be written more cleanly as funcobj.__kwdefaults__ = dict(kwdefaults).

this breaks teleportation compatibility across different RPyC versions
If you are referring to #387, I think it is out of scope. Your changes do fix the unit tests you added:

$ docker exec -it rpyc-3.7 /opt/rpyc/bin/rpyc_classic.py --host 0.0.0.0
$ docker exec -it rpyc-3.6 python -c "exec('def kwdefaults(pos=5, *, a=42, b=\'bye\', c=(12.4, )):\n    return pos, a, b, c\n');import socket;import rpyc;addr = socket.gethostbyname('rpyc-3.7');conn = rpyc.classic.connect(addr, port=18812); remote_kwdefaults = rpyc.utils.classic.teleport_function(conn, kwdefaults); print(remote_kwdefaults(pos=1))"

Thank you for the contribution!

[Jongy]

Everything looks pretty good. I'll probably make some minor changes like reducing some accidental complexity I found---funcobj.__kwdefaults__ = {t[0]: t[1] for t in kwdefaults} could be written more cleanly as funcobj.__kwdefaults__ = dict(kwdefaults).

Hmm you're right, I forgot dict() can be used this way. Anyway it's not the hot area of RPyC, I guess, so less important to make efficient. For readability's sake, tho...

If you are referring to #387, I think it is out of scope. Your changes do fix the unit tests you added:

$ docker exec -it rpyc-3.7 /opt/rpyc/bin/rpyc_classic.py --host 0.0.0.0
$ docker exec -it rpyc-3.6 python -c "exec('def kwdefaults(pos=5, *, a=42, b=\'bye\', c=(12.4, )):\n    return pos, a, b, c\n');import socket;import rpyc;addr = socket.gethostbyname('rpyc-3.7');conn = rpyc.classic.connect(addr, port=18812); remote_kwdefaults = rpyc.utils.classic.teleport_function(conn, kwdefaults); print(remote_kwdefaults(pos=1))"

I was referring to cross RPyC versions, not cross CPython; Because now export_function & import_function work with tuples of 5 items, but these used to be 4 items, so if I try to teleport a function from RPyC master to the previous tag, I will get an error in import_function for trying to unpack a 5-tuple into 4 names.

I guess it can be easily solved by expecting this ValueError, catching it and calling import_function again without kwdefaults, but like I said, I don't know if cross-version is a goal of RPyC, so I haven't added it in this PR.

Thank you for the contribution!

Thanks for the quick review and merge :)

[comrumino]

I released RPyC 5.0.0 today. Per semantic versioning users should expect breaks in backwards compatibility. Of course, I'll add a note in the release description regarding teleport function not being backwards compatibility. Thank you for your work and explanation!