Iso-duration

[constantinius]

Proper ISO 8601 duration encoding for temporal dimension steps

[gadomski]

Marking as draft until #10 is merged, as this includes the diff from that.

[gadomski]

Is https://pypi.org/project/isoduration/ usable? If there's an off-the-shelf package that we can lean on, that'd be preferable to a re-implementation IMO.

I ran into the same issue in noaa-cdr: https://github.com/stactools-packages/noaa-cdr/blob/db4ebdc633a2cb1f27874b039edcbe761b81b214/src/stactools/noaa_cdr/time.py#L191-L215. There, I knew I had a limited subset of cases to handle, so I did re-implement, but since this is supposed to be a general-use library, we should avoid re-implementation if possible IMO.

[constantinius]

After some investigation I can say: unfortunately isoduration does not provide the arithmetic operations on their central Duration class that we need in this case.

The other option pandas.Timedelta is quite a heavy dependency and also does not cover all the bases.

For temporal dimensions we have a single conversion from timedelta to an ISO duration, which I hope is covered by the function. I would love to go ahead with this.

[gadomski]

iso_duration deserves some unit tests, I think, to ensure we're handling some common cases properly. At minimum:

• One year
• One month
• One day
• One week
• One hour
• One second
• A duration that has everything
• A duration that doesn't have any hours, minutes, or seconds

That will help future developers understand the expected behavior of the function.

Question: do we need a reverse function, one that parses a string into a timedelta?

[constantinius]

Question: do we need a reverse function, one that parses a string into a timedelta?

This has not yet come up. Currently we are building te timedeltas from netcdf/zarr metadata. They are usually expressed as somthing like "days since 1990-01-01"

[constantinius]

I added a couple of unit-tests

[gadomski]

Appreciate the fixups, looks good!

[gadomski]

@constantinius this is not passing CI so needs fixes before it can go in and we release.