Simon Willison’s Weblog

California Clock Change. The clocks go back in California tonight and I finally built my dream application for helping me remember if I get an hour extra of sleep or not, using a Claude Artifact. Here's the transcript.

This is one of my favorite examples yet of the kind of tiny low stakes utilities I'm building with Claude Artifacts because the friction involved in churning out a working application has dropped almost to zero.

(I added another feature: it now includes a note of what time my Dog thinks it is if the clocks have recently changed.)

# 3rd November 2024, 5:11 am / claude-artifacts, ai-assisted-programming, projects, ai, timezones, llms

Australia/Lord_Howe is the weirdest timezone (via) Lord Howe Island - part of Australia, population 382 - is unique in that the island's standard time zone is UTC+10:30 but is UTC+11 when daylight saving time applies. It's the only time zone where DST represents a 30 minute offset.

# 31st October 2024, 10:03 pm / timezones

sqlite-jiff (via) I linked to the brand new Jiff datetime library yesterday. Alex Garcia has already used it for an experimental SQLite extension providing a timezone-aware jiff_duration() function - a useful new capability since SQLite's built in date functions don't handle timezones at all.

select jiff_duration(
  '2024-11-02T01:59:59[America/Los_Angeles]',
  '2024-11-02T02:00:01[America/New_York]',
  'minutes'
) as result; -- returns 179.966

The implementation is 65 lines of Rust.

# 23rd July 2024, 3:53 am / timezones, rust, sqlite, alex-garcia

Jiff (via) Andrew Gallant (aka BurntSushi) implemented regex for Rust and built the fabulous ripgrep, so it's worth paying attention to their new projects.

Jiff is a brand new datetime library for Rust which focuses on "providing high level datetime primitives that are difficult to misuse and have reasonable performance". The API design is heavily inspired by the Temporal proposal for JavaScript.

The core type provided by Jiff is Zoned, best imagine as a 96-bit integer nanosecond time since the Unix each combined with a geographic region timezone and a civil/local calendar date and clock time.

The documentation is comprehensive and a fascinating read if you're interested in API design and timezones.

# 22nd July 2024, 4:48 am / api-design, rust, timezones, andrew-gallant

It’s Time For A Change: datetime.utcnow() Is Now Deprecated (via) Miguel Grinberg explains the deprecation of datetime.utcnow() and utcfromtimestamp() in Python 3.12, since they return naive datetime objects which cause all sorts of follow-on problems.

The replacement idiom is datetime.datetime.now(datetime.timezone.utc)

# 18th November 2023, 7:24 pm / timezones, python

Benjamin “Zags” Zagorsky: Handling Timezones in Python. The talks from PyCon US have started appearing on YouTube. I found this one really useful for shoring up my Python timezone knowledge: It reminds that if your code calls datetime.now(), datetime.utcnow() or date.today(), you have timezone bugs—you’ve been working with ambiguous representations of instances in time that could span a 26 hour interval from UTC-12 to UTC+14. date.today() represents a 24 hour period and hence is prone to timezone surprises as well. My code has a lot of timezone bugs!

# 26th May 2022, 3:40 am / pycon, timezones, python

Temporal: getting started with JavaScript’s new date time API. Axel Rauschmayer explores the new proposed API for handling dates, times and timezones in JavaScript., which is under development by Ecma TC39 at the moment (and made available as a Polyfill which you are recommended not to run in production since the API is still being figured out). This is a notoriously difficult problem so it’s always interesting to see the latest thinking on how to best address it.

# 7th July 2021, 10:29 pm / javascript, timezones, datetime

Big tech warns of ’Japan’s millennium bug’ ahead of Akihito’s abdication (via) Emperor Akihito’s abdication in April 2019 triggers a new era, and the Japanese calendar counts years from the coronation of the current emperor. The era hasn’t changed since 1989 and a great deal of software is unable to handle a change. To make things more complicated... the name of the new era will be announced in late February, but it needs to be represented in unicode as a single new character... and the next version of Unicode (v12) is due out in early March. There may have to be a Unicode 12.1 released shortly afterwards that includes the new codepoint.

# 28th July 2018, 2:04 pm / unicode, timezones, japan

django-timezones. Models, form fields and a template filter for dealing with timezones in Django.

# 21st August 2008, 11:18 pm / django, timezones, python

What’s New in Edge Rails: Easier Timezones (via) Time zones can be a nightmare to get right—if this works well it’s going to make a lot of people’s lives a whole bunch easier.

# 2nd April 2008, 3:39 pm / timezones, rails

calendar.timegm() (via) An “unrelated but handy function” that converts a time.gmtime() in to a corresponding Unix timestamp. I’ve been hand-rolling this one for years; never thought to look in calendar.

# 3rd September 2007, 1:54 am / python, sam-ruby, calendar, timezones, datetime, unixtimestamp, time

Django vs feedparser on dates. Some useful tips in the comments. I find Python’s timezone stuff endlessly frustrating: I know it can do what I want, but it always takes me a ridiculously long time to figure out the necessary incantations.

# 2nd September 2007, 10:17 am / python, datetime, django, feedparser, timezones

A Zoned Defense. Using JavaScript’s date.getTimezoneOffset() to detect the user’s timezone and stash it in a cookie.

# 20th March 2007, 9:51 am / timezones, javascript