Use QTable for IERS throughout

[mhvk]

#9204 made me look at the IERS code again and I realized it could use some cleanup. The first commit ensures we just use QTable rather than go through Table and then fill the masked columns. This makes merging/selecting between A and B quite a bit cleaner. The second commit removes the IERS.read method (which was just assigned to IERS_B.read) so that super class work; it also prevents warnings about dropped masks.

A small additional change is to ensure that in Time the default IERS table is always that from IERS_Auto.

cc @aarchiba

[taldcroft]

This looks basically fine. In your local testing have you ensured that networking is enabled (no tests are skipped)?

Should we deprecate the bare IERS class now? I expect that if you were writing this whole thing today that it would look very different.

[taldcroft]

This is a creative / funky use of searchsorted. Is this guaranteed to always work or does it just happen to work for the current implementation. It depends on a numerical ordering of True and False.

[mhvk]

It is a lot faster as it doesn't have to allocate an array of indices. And I think False == 0 and True == 1 is sufficiently baked into python...
In fact, one can do the searchsorted on the flag, which changes the whole thing from ~250 us to 3.5 us...

%timeit is_predictive = (table['UT1Flag_A'] == 'P') | (table['PolPMFlag_A'] == 'P'); np.min(np.flatnonzero(is_predictive))
# 1000 loops, best of 5: 238 µs per loop
%timeit min(np.searchsorted(table['UT1Flag_A'], 'P'), np.searchsorted(table['PolPMFlag_A'], 'P'))
# 100000 loops, best of 5: 3.49 µs per loop

[taldcroft]

Should this test just use both IERS and IERS_B as a test parameter? That would remove the need for the new test_iers_b_for_iers.

[mhvk]

Good point, done.

[mhvk]

@taldcroft - I thought about deprecating the bare IERS class - really, it should have been an IERSBase in the first place - but ended up thinking it might be better done as part of #9227 (triggered by the issues raised by @aarchiba).

p.s. And, yes, I tested locally with networking enabled and with a local finals file (a test that never gets done in CI - another thing I would now have done differently!)

[bsipocz]

p.s. And, yes, I tested locally with networking enabled and with a local finals file (a test that never gets done in CI - another thing I would now have done differently!)

do we have an issue opened for it? maybe at some point someone has the time to come up for a CI solution for this corner case.

[taldcroft]

@mhvk - looks good to merge to me if you think it's done.

[mhvk]

@bsipocz - see #9232.

Merging this one, thanks for the review, @taldcroft.