[Twisted-Python] Some things I've learned: safer callbacks, better t.p.context

[Itamar Turner-Trauring]

Not been doing much Twisted lately, but have been doing async stuff
elsewhere, and I've learned some useful things.

1. Callbacks should be sync or async, but never
sometimes-one-sometimes-the-other. For details go read
http://blog.ometer.com/2011/07/24/callbacks-synchronous-and-asynchronous/.
For example, Deferred.addCallback(f) really should never run f()
immediately.

3. By instrumenting all callbacks it manages, which may or may not
require item #1, Twisted can have a context that automatically follows
callbacks. Node has this and it is extremely useful.
http://fredkschott.com/post/2014/02/conquering-asynchronous-context-with-cls/
is best summary I've found with a bit of searching.

-- 
Itamar Turner-Trauring