Side-note: Django 4.0 will switch from using pytz to using the standard library zoneinfo module introduced in Python 3.9, which has a backport that works as far back as 3.6: https://github.com/pganssle/zoneinfo (https://pypi.org/project/backports.zoneinfo/)

If I need to handle timezones I'll use that, but I think I can get away without it?

Django does this: https://github.com/django/django/blob/b0ed619303d2fb723330ca9efa3acf23d49f1d19/setup.cfg#L39-L43

install_requires = asgiref >= 3.3.2 backports.zoneinfo; python_version<"3.9" sqlparse >= 0.2.2 tzdata; sys_platform == 'win32'

The audiences I care about here are:

• Producers of this timestamp - generally that will be users who are using datasette publish to share their data
• Human consumers of this timestamp - end users who look at a Datasette site and want to know how recent the data is
• Machine consumers of this timestamp - API integrations that might want to check if a Datasette instance has been updated before downloading new data

For producers I think there are going to be two categories. The first is users who run "publish" and want the site to reflect when they did so (probably using --updated=now when they publish). The second are users who are willing to spend more time thinking about this - for example my various git scraping projects where I want to use a date derived from the git history.

For humans... I'd like to be able to calculate a relative time (3 hours ago) in addition to showing the display time, because that helps avoid confusion over timezones.

For machine consumers, it might be nice to offer the option of a calculated Unix timestamp-since-1970, since those can be easier to work with in some languages than running a full ISO date parser.

The simplest possible version of this: it's always represented as a UTC ISO datetime, like this:

"updated": "2020-10-31T12:00:00+00:00"

Later versions of Datasette could extend this to handle other timezones or support just the date (though that's a backwards incompatible change so probably better to decide on the date thing right now).

So this is a metadata key called updated which can be applied at the table, database or instance level. It is represented as a .isoformat() timestamp.

Question: should I support just the date - yyyy-mm-dd - in addition to the datetime?

I think so. I can easily imagine situations where the exact time of day that a change was made hasn't been recorded, but the overall date is known.

But in that case, should the updated key sometimes be yyyy-mm-dd and sometimes be the full isoformat datetime? Or should there be an updated_date key that's used for just the date?

I'm going to use https://github.com/dateutil/dateutil for this - it's been maintained constantly (by an evolving team of contributors) since 2003 and is a very trustworthy dependency.

Thanks for this!

Codecov Report

Merging #1476 (2eb01ff) into main (b28b6cd) will not change coverage. The diff coverage is n/a.

```diff @@ Coverage Diff @@

main #1476 +/-

======================================= Coverage 91.83% 91.83%
======================================= Files 34 34
Lines 4421 4421
======================================= Hits 4060 4060
Misses 361 361
```

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