Compatiblity with CFTime

[rabernat]

I am trying to catalog climate model data stored in Zarr format on Google Cloud / AWS using STAC. My approach is to create a STAC collection for each Zarr dataset and link to the Zarr data using collection-level assets (see related discussion @ radiantearth/stac-spec#781).

I have hit a tiny snag with datetimes. I need to populate temporal_extent for the collections. I get this by reading the dataset's time range. The times are encoded using the CF Conventions for time coordinates. In python, CF times are implemented by the cftime package. cftime provides a (mostly) duck-type compatible with datetime. However, cftime has no .tzinfo attribute.

This tiny change allows pystac to work with cftime datetimes.

I have not added a test because I didn't want to add cftime to the dependencies. One could possibly use a mock to test this feature. Or we could merge this tiny change with no test. I'll follow whatever path the devs recommend.

cc @charlesbluca

[codecov-io]

Codecov Report

Merging #238 into develop will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop     #238   +/-   ##
========================================
  Coverage    93.73%   93.73%           
========================================
  Files           30       30           
  Lines         3749     3749           
========================================
  Hits          3514     3514           
  Misses         235      235           

Impacted Files	Coverage Δ
pystac/utils.py	97.70% <100.00%> (ø)

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[rabernat]

Could the maintainers (maybe @lossyrob) let me know whether this PR might be acceptable. I'd be happy to make any changes required.

[lossyrob]

@rabernat apologies for the delay in review.

The change looks great, however can you provide a unit test that demostrates the failure case when this change is not in place/succeeds with this change? Thanks!

[rabernat]

The change looks great, however can you provide a unit test that demostrates the failure case when this change is not in place/succeeds with this change?

Sure. Would you prefer I add cftime as a test dependency or that I use some kind of mock / monkeypatch to datetime?

[lossyrob]

I think the mock/monkeypatch version would work, with a comment pointing at the specific cftime class it is mimicking in case API changes down the road. Thanks!

[rabernat]

After thinking this through, I decided it made more sense to fix this in cftime, rather than pystac. See Unidata/cftime#209. But thanks for considering this.