No problem with this one overall. I wonder if our local UTC should be an alias of pytz.utc, IFF pytz is importable (to avoid having more than one global for the zone).

@tseaver RE: default to using pytz, default to ours. Good call!

Code reviews are so useful 😄 I totally overlooked that and it's totally the right way to go.

I figured that dropping pytz was really FBO users who never care about timezones at all: those who do will want it, anyway.

Yeah for sure.

@tseaver I re-pushed the initial commit. Sorry I finished it awhile ago but forgot to push.

Wanted to actually test the case that pytz was installed, but it was being too big a PITA to deal with sys.modules. WDYT?

We could add a tox stanza that didn't install it.

What is that?

Oops, I inverted it in my mind: we could add a stanza that tests it w/ pytz installed, e.g.:

[testenv:py27_w_extras]
deps =
    {[testenv]deps}
    pytz

Can we punt on it for this PR and fix address it after?

Sure.

The only thing I see which might be gating is we have no explicit test coverage for the _UTC class: do we need it? If not, go ahead and merge.

I added it to test__helpers.py, been in here for awhile.

LGTM