Django and Time Zones: New in the Trunk

Presentation I gave during Pykonik meet-up (December 2011)
http://blog.pykonik.org/2011/11/grudniowe-spotkanie-december-meetup.html

Transcript

1. Django and Time Zones New in trunk Tomek Paczkowski @oinopion December 2011
2. Time zones are a lie.
3. Time zones are a lie. Sundials
4. Time zones are a lie. Sundials XIX century – Railroad time
5. Time zones are a lie. Sundials XIX century – Railroad time Artificial division
6. Time zones are a lie. Sundials XIX century – Railroad time Artificial division Humans think in local time
7. Time zones are a lie. Sundials XIX century – Railroad time Artificial division Humans think in local time Time as a point in continuum
8. DST: Dreadful Summer Time
9. DST: Dreadful Summer Time Promises of savings beyond comprehension ...
10. DST: Dreadful Summer Time Promises of savings beyond comprehension ... ... and more sunlit leisure
11. DST: Dreadful Summer Time Promises of savings beyond comprehension ... ... and more sunlit leisure Artificial division, even more political
12. DST: Dreadful Summer Time Promises of savings beyond comprehension ... ... and more sunlit leisure Artificial division, even more political No reliably measured savings
13. DST: Dreadful Summer Time Promises of savings beyond comprehension ... ... and more sunlit leisure Artificial division, even more political No reliably measured savings Reliably measured raise in suicides
14. Time is hard. Let’s go shopping
15. Time is hard. Let’s go shopping UTC = GMT
16. Time is hard. Let’s go shopping UTC = GMT CET → CEST
17. Time is hard. Let’s go shopping UTC = GMT CET → CEST (27/03/2011 2:30?)
18. Time is hard. Let’s go shopping UTC = GMT CET → CEST (27/03/2011 2:30?) CET ← CEST
19. Time is hard. Let’s go shopping UTC = GMT CET → CEST (27/03/2011 2:30?) CET ← CEST (30/10/2011 2a:30)
20. Time is hard. Let’s go shopping UTC = GMT CET → CEST (27/03/2011 2:30?) CET ← CEST (30/10/2011 2a:30) CET/CEST vs Warsaw Mean Time
21. Time is hard. Let’s go shopping UTC = GMT CET → CEST (27/03/2011 2:30?) CET ← CEST (30/10/2011 2a:30) CET/CEST vs Warsaw Mean Time (+1:24)
22. Time is hard. Let’s go shopping UTC = GMT CET → CEST (27/03/2011 2:30?) CET ← CEST (30/10/2011 2a:30) CET/CEST vs Warsaw Mean Time (+1:24) Future dates
23. Code, dammit!
24. Code, dammit! Python and datetime
25. Code, dammit! Python and datetime, time
26. Code, dammit! Python and datetime, time, calendar...
27. Code, dammit! Python and datetime, time, calendar... Abstract tzinfo class, but no implementations
28. Code, dammit! Python and datetime, time, calendar... Abstract tzinfo class, but no implementations datetime.utcnow().tzinfo is None
29. Code, dammit! Python and datetime, time, calendar... Abstract tzinfo class, but no implementations datetime.utcnow().tzinfo is None datetime(2011, 3, 27, 2, 30, tzinfo=CET) # never happend, but no error
30. pytz is the hero
31. pytz is the hero Olson’s database
32. pytz is the hero Olson’s database cet = pytz.timezone(’Europe/Warsaw’)
33. pytz is the hero Olson’s database cet = pytz.timezone(’Europe/Warsaw’) cet.localize(datetime(2011, 10, 30, 2, 30), is_dst=True)
34. pytz is the hero Olson’s database cet = pytz.timezone(’Europe/Warsaw’) cet.localize(datetime(2011, 10, 30, 2, 30), is_dst=True) utc_dt.astimezone(cet)
35. Old times
36. Old times TIME_ZONE = "America/Chicago"
37. Old times TIME_ZONE = "America/Chicago" Manual conversions
38. Old times TIME_ZONE = "America/Chicago" Manual conversions https://github.com/brosner/django-timezones/
39. Django+01:40
40. Django+01:40 USE_TZ = True
41. Django+01:40 USE_TZ = True django.timezone.activate(tz_name)
42. Django+01:40 USE_TZ = True django.timezone.activate(tz_name) Done!
43. Django+01:40 USE_TZ = True django.timezone.activate(tz_name) Done! Suggestion: use middleware
44. Django+01:40 USE_TZ = True django.timezone.activate(tz_name) Done! Suggestion: use middleware Use template tags and filters to change
45. Twitz class Profile(models.Model): user = models.OneToOneField(User) time_zone = models.CharField(max_length=200, blank=True) @receiver(post_save, sender=User) def create_user_profile(sender, instance, created, **kwargs): if created: Profile.objects.create(user=instance)
46. Twitz class SettingsView(UpdateView): template_name = ’accounts/settings.html’ form_class = SettingsForm def get_object(self, queryset=None): return self.request.user.profile def get_success_url(self): return reverse(’settings’) settings = login_required(SettingsView.as_view())
47. Twitz {{ status.pub_date|timezone:other_user_tz }} {% timezone other_user_tz %} <strong>{% now "r" %}</strong> {% endtimezone %}
48. Twitz class TimeZoneMiddleware: def process_request(self, request): user = request.user if user.is_authenticated(): try: timezone.activate(user.profile.time_zone) except (UnknownTimeZoneError, ValueError) as e: logger.warn("Error setting time zone: %s", e)
49. How it works
50. How it works Thread-locals
51. How it works Thread-locals All dates converted on output (templates)
52. How it works Thread-locals All dates converted on output (templates) All dates converted on input (forms)
53. How it works Thread-locals All dates converted on output (templates) All dates converted on input (forms) Database stores everything in UTC
54. How it works Thread-locals All dates converted on output (templates) All dates converted on input (forms) Database stores everything in UTC Migration: consult your database manual.
55. How it works Thread-locals All dates converted on output (templates) All dates converted on input (forms) Database stores everything in UTC Migration: consult your database manual. ... PostgreSQL: no migration needed
56. External world
57. External world Remember to utc.localize()
58. External world Remember to utc.localize() Watch out for invalid dates (is_dst=None)
59. That’s all, folks! Questions?
60. That’s all, folks! Questions? Thank you! https://github.com/oinopion/twitz