Replace use of pytz with built-in timezone

Now that we're on Python 3.10, we can just use the built-in `timezone`
module instead of installing `pytz`.

`pytz` remains a Django dependency (for now), but we at least can remove
our direct dependence on it.

pyproject.toml

@@ -50,15 +50,13 @@ freezegun = "*"
 isort = { version = "^5.8", extras = ["pyproject"] }  # Version 5 introduces black compatibility
 lxml = "*"
 pylint = "^2.8"
-pytz = "*"  # (It's a production dependency by way of Django, but used directly in tests)
 responses = "*"
 
 # Dependencies for static type checking
 django-stubs = { version = "^1.9" }
 mypy = { version = "*"}
 types-certifi = { version = "*" }
 types-cryptography = { version = "*" }
-types-pytz = { version = "*" }
 types-requests = { version = "*" }
 
 # Dependencies helpful for local development, not used otherwise

ws/settings.py

@@ -2,7 +2,7 @@
 Django settings for ws project.
 
 For more information on this file, see
-https://docs.djangoproject.com/en/2.2/topics/settings/
+https://docs.djangoproject.com/en/3.2/topics/settings/
 """
 
 # Build paths inside the project like this: os.path.join(BASE_DIR, ...)

ws/tests/factories.py

@@ -1,9 +1,8 @@
-from datetime import datetime, timedelta
+from datetime import datetime, timedelta, timezone
 
 import allauth.account.models as account_models
 import factory
 import factory.fuzzy
-import pytz
 from factory.django import DjangoModelFactory
 from mitoc_const import affiliations
 
@@ -138,7 +137,7 @@ class Meta:
 
     participant = factory.SubFactory(ParticipantFactory)
     reminder_sent_at = factory.fuzzy.FuzzyDateTime(
-        start_dt=datetime(2021, 11, 13, tzinfo=pytz.UTC)
+        start_dt=datetime(2021, 11, 13, tzinfo=timezone.utc)
     )
 
 

ws/tests/test_merge.py

@@ -1,7 +1,6 @@
 import unittest
-from datetime import datetime
+from datetime import datetime, timezone
 
-import pytz
 from django.contrib.auth.models import Permission, User
 from django.db import connections
 from django.db.utils import IntegrityError
@@ -145,10 +144,10 @@ def test_password_quality(self):
 
     def test_membership_reminders(self):
         """The newest reminder is honored, even if delivered to the older participant."""
-        newer_reminder_sent_at = datetime(2020, 12, 25, tzinfo=pytz.UTC)
+        newer_reminder_sent_at = datetime(2020, 12, 25, tzinfo=timezone.utc)
         factories.MembershipReminderFactory.create(
             participant=self.tim,
-            reminder_sent_at=datetime(2020, 10, 1, tzinfo=pytz.UTC),
+            reminder_sent_at=datetime(2020, 10, 1, tzinfo=timezone.utc),
         )
         factories.MembershipReminderFactory.create(
             participant=self.old,

ws/tests/test_tasks.py

@@ -1,8 +1,7 @@
-from datetime import date, datetime
+from datetime import date, datetime, timezone
 from unittest import mock
 from unittest.mock import patch
 
-import pytz
 from django.core import mail
 from django.core.cache import cache
 from django.test import SimpleTestCase
@@ -246,7 +245,7 @@ def test_nobody_needs_reminding():
         )
         factories.MembershipReminderFactory.create(
             participant=already_reminded,
-            reminder_sent_at=datetime(2020, 12, 25, tzinfo=pytz.UTC),
+            reminder_sent_at=datetime(2020, 12, 25, tzinfo=timezone.utc),
         )
 
         with patch.object(tasks.remind_lapsed_participant_to_renew, 'delay') as email:
@@ -272,7 +271,7 @@ def test_can_be_reminded_once_a_year():
         # We reminded them once before, but it was for the previous year's membership
         factories.MembershipReminderFactory.create(
             participant=par,
-            reminder_sent_at=datetime(2017, 12, 25, tzinfo=pytz.UTC),
+            reminder_sent_at=datetime(2017, 12, 25, tzinfo=timezone.utc),
         )
         with patch.object(tasks.remind_lapsed_participant_to_renew, 'delay') as email:
             tasks.remind_participants_to_renew()
@@ -298,7 +297,7 @@ def test_success(self):
         )
         self.assertEqual(reminder.participant, par)
         self.assertEqual(
-            reminder.reminder_sent_at, datetime(2019, 1, 25, 17, 0, tzinfo=pytz.UTC)
+            reminder.reminder_sent_at, datetime(2019, 1, 25, 17, 0, tzinfo=timezone.utc)
         )
 
     def test_idempotent(self):
@@ -336,7 +335,7 @@ def test_tried_to_remind_again_too_soon(self):
         )
         factories.MembershipReminderFactory.create(
             participant=par,
-            reminder_sent_at=datetime(2018, 4, 25, tzinfo=pytz.UTC),
+            reminder_sent_at=datetime(2018, 4, 25, tzinfo=timezone.utc),
         )
 
         with patch.object(renew, 'send_email_reminding_to_renew') as email:

ws/tests/utils/test_dates.py

@@ -2,7 +2,6 @@
 from unittest import mock
 from zoneinfo import ZoneInfo
 
-import pytz
 from freezegun import freeze_time
 
 from ws import enums
@@ -123,27 +122,27 @@ def test_closest_wednesday(self, local_now):
                 self.assertLess(test_date, closest_wed)
 
     def test_closest_wed_at_noon(self):
-        est = pytz.timezone('America/New_York')
+        eastern = ZoneInfo('America/New_York')
 
         # On Wednesday, we return the same day
         with freeze_time("2016-12-28 23:22 EST"):
             self.assertEqual(
                 date_utils.closest_wed_at_noon(),
-                est.localize(datetime(2016, 12, 28, 12, 0, 0)),
+                datetime(2016, 12, 28, 12, 0, 0, tzinfo=eastern),
             )
 
         # 3 days to the next Wednesday, 4 days to the previous
         with freeze_time("2016-12-25 10:00 EST"):
             self.assertEqual(
                 date_utils.closest_wed_at_noon(),
-                est.localize(datetime(2016, 12, 28, 12, 0, 0)),
+                datetime(2016, 12, 28, 12, 0, 0, tzinfo=eastern),
             )
 
         # 4 days to the next Wednesday, 3 days to the previous
         with freeze_time("2016-12-24 10:00 EST"):
             self.assertEqual(
                 date_utils.closest_wed_at_noon(),
-                est.localize(datetime(2016, 12, 21, 12, 0, 0)),
+                datetime(2016, 12, 21, 12, 0, 0, tzinfo=eastern),
             )
 
     def test_is_currently_iap(self):
@@ -165,8 +164,8 @@ def test_is_currently_iap(self):
             self.assertFalse(date_utils.is_currently_iap())
 
     def test_fcfs_close_time(self):
-        est = pytz.timezone('America/New_York')
-        thur_night = est.localize(datetime(2019, 1, 24, 23, 59, 59))
+        eastern = ZoneInfo("America/New_York")
+        thur_night = datetime(2019, 1, 24, 23, 59, 59, tzinfo=eastern)
 
         # For the usual case (trips over the weekend), it's the Thursday beforehand
         (fri, sat, sun, mon) = (date(2019, 1, dom) for dom in [25, 26, 27, 28])
@@ -187,9 +186,9 @@ def test_fcfs_close_time(self):
         self.assertEqual(date_utils.fcfs_close_time(date(2019, 1, 24)), wed_night)
 
     def test_next_lottery(self):
-        est = pytz.timezone('America/New_York')
-        friday_the_23rd = est.localize(datetime(2019, 1, 23, 9, 0, 0))
-        friday_the_30th = est.localize(datetime(2019, 1, 30, 9, 0, 0))
+        eastern = ZoneInfo("America/New_York")
+        friday_the_23rd = datetime(2019, 1, 23, 9, 0, 0, tzinfo=eastern)
+        friday_the_30th = datetime(2019, 1, 30, 9, 0, 0, tzinfo=eastern)
 
         # Normal cases: lottery is always just the next Wednesday morning
         with freeze_time("Fri, 25 Jan 2019 03:00:00 EST"):

ws/tests/views/test_account.py

@@ -1,5 +1,5 @@
 import uuid
-from datetime import datetime
+from datetime import datetime, timezone
 from unittest import mock
 
 import pytz
@@ -73,7 +73,7 @@ def test_known_bad_password(self, mocked_settings):
         self.assertFalse(quality.is_insecure)
         self.assertEqual(
             quality.last_checked,
-            datetime(2019, 8, 29, 16, 25, tzinfo=pytz.utc),
+            datetime(2019, 8, 29, 16, 25, tzinfo=timezone.utc),
         )
 
         # Log in again, but this time with DEBUG off (& whitelist still present)
@@ -111,7 +111,7 @@ def test_previously_secure_password(self):
         self.assertTrue(quality.is_insecure)
         self.assertEqual(
             quality.last_checked,
-            datetime(2019, 8, 29, 16, 25, tzinfo=pytz.utc),
+            datetime(2019, 8, 29, 16, 25, tzinfo=timezone.utc),
         )
 
         # Because the user's password is insecure, they're prompted to change it
@@ -162,7 +162,7 @@ def test_password_is_marked_secure(self):
         self.assertFalse(participant.passwordquality.is_insecure)
         self.assertEqual(
             participant.passwordquality.last_checked,
-            datetime(2019, 8, 29, 16, 25, tzinfo=pytz.utc),
+            datetime(2019, 8, 29, 16, 25, tzinfo=timezone.utc),
         )
 
     def test_redirect_should_be_preserved(self):
@@ -218,7 +218,7 @@ def test_change_password_fram_insecure(self):
         self.assertFalse(par.passwordquality.is_insecure)
         self.assertEqual(
             par.passwordquality.last_checked,
-            datetime(2019, 7, 15, 16, 45, tzinfo=pytz.utc),
+            datetime(2019, 7, 15, 16, 45, tzinfo=timezone.utc),
         )
 
     def test_user_without_participant(self):

ws/tests/views/test_participant.py

@@ -1,5 +1,5 @@
 import random
-from datetime import date, datetime
+from datetime import date, datetime, timezone
 from unittest import mock
 
 import pytz
@@ -317,7 +317,7 @@ def test_new_participant(self):
         task_update.delay.assert_called_with(participant.pk)
 
         # We then update the timestamps!
-        now = datetime(2019, 2, 15, 17, 25, tzinfo=pytz.utc)
+        now = datetime(2019, 2, 15, 17, 25, tzinfo=timezone.utc)
         self.assertEqual(participant.last_updated, now)
         # Since the participant modified their own profile, we save `profile_last_updated`
         self.assertEqual(participant.profile_last_updated, now)

ws/utils/dates.py

@@ -16,8 +16,7 @@ def localize(dt_time: datetime) -> datetime:
     >>> localize(datetime(2018, 10, 27, 4, 30)
     datetime.datetime(2018, 10, 27, 4, 30, tzinfo=<DstTzInfo 'America/New_York' EDT-1 day, 20:00:00 DST>)
     """
-    pytz_timezone = timezone.get_default_timezone()
-    return pytz_timezone.localize(dt_time)
+    return timezone.get_default_timezone().localize(dt_time)
 
 
 def itinerary_available_at(trip_date: date) -> datetime: