Support LowLevelCallable

[sklam]

Fix #2995

• add ctypes lowlevelcallable
• add cffi lowlevelcallable
• support .user_data

[seibert]

This creates an import cycle, which appears to be handled properly in Python 3, but not Python 2.

[codecov-io]

Codecov Report

Merging #2999 into master will increase coverage by <.01%.
The diff coverage is 89.79%.

@@            Coverage Diff             @@
##           master    #2999      +/-   ##
==========================================
+ Coverage   85.73%   85.74%   +<.01%     
==========================================
  Files         327      331       +4     
  Lines       68535    68630      +95     
  Branches     7755     7759       +4     
==========================================
+ Hits        58760    58845      +85     
- Misses       8535     8544       +9     
- Partials     1240     1241       +1

[pv]

xref #2995 (comment)

[dhirschfeld]

I'm very keen on this functionality and it seems like it's very nearly there so I'm curious if it will make the cutoff for 0.40.0?

[dhirschfeld]

Ping! It seems like this PR is most of the way there. Is there anything in particular holding it up?

I'm hopeful that it will resolve #2578 as well.

[pv]

My comment at #2995 (comment) is not addressed so far at least.

[github-actions]

This pull request is marked as stale as it has had no activity in the past 3 months. Please respond to this comment if you're still interested in working on this. Many thanks!

[jfbourdon]

It would be sad to see this being closed... but well, as a simple occasional user I'm really not the one who can help and I won't pretend understanding a single line of code behind this PR!

[github-actions]

This pull request is marked as stale as it has had no activity in the past 3 months. Please respond to this comment if you're still interested in working on this. Many thanks!