[Twisted-Python] qt5 and twisted, reactor already installed, python 2.x

[meejah]

Glyph Lefkowitz <glyph at twistedmatrix.com> writes:

> Yes.  Unfortunately, lots of places do import the reactor directly
> today, but we have long since decided that this is a bad way to do
> things.  This is why e.g. react
> <https://twistedmatrix.com/documents/16.2.0/api/twisted.internet.task.h
> tml#react> passes the reactor to your function as a parameter, so you
> can pass it on down to any other code that needs it.

As a "casual" user of Twisted, I was somewhat skeptical of this "pass
the reactor everywhere" approach -- but I did try to follow this advice
in txtorcon, and was rewarded with easy-to-write tests regarding timing,
which are (usually) a horror-show *and* I was rewarded with having to
think about "do I *really* need the reactor here?".

Now, sometimes you can compromise. For example, see my AddrMap class
which assigns a "self.scheduler" which is usually just gotten by
importing from twisted.internet.reactor -- *but* critically, the tests
can re-assign this:

   https://github.com/meejah/txtorcon/blob/master/test/test_addrmap.py#L109

Ideally, this would have been passed-in via the __init__ but,
*shruggy-face*. The point being, you can incrementally upgrade to "the
better way".

Overall, I'm very sold on accessing "the reactor" via "self dot
something" rather than via imports *even if* the only reason ends up
being "because testing". It's pretty likely that some random user you've
never heard of has a similar use-case to that thing you needed to do in
that one test... (I've read this elsewhere, not my idea)

If nothing else, it will cause you to pause and consider "how will this
thing access the reactor", which will cause you to think about
concurrency issues... (Or, contrary-wise, classes which *don't* have a
self._reactor definitely do *not* need any thinking about concurrency --
which is also a big win).

In any case, my concurrency-hackles raise when I see ".. import
reactor". Best to localize these fears to "self._reactor".

-- 
meejah