timezone: Use standard library datetime.timezone.utc consistently.

datetime.timezone is available in Python ≥ 3.2.  This also lets us
remove a pytz dependency from the PostgreSQL scripts.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

analytics/management/commands/analyze_user_activity.py

@@ -2,14 +2,13 @@ import datetime
 from typing import Any, Dict
 
 from django.core.management.base import BaseCommand, CommandParser
-from django.utils.timezone import utc
 
 from zerver.lib.statistics import seconds_usage_between
 from zerver.models import UserProfile
 
 
 def analyze_activity(options: Dict[str, Any]) -> None:
-    day_start = datetime.datetime.strptime(options["date"], "%Y-%m-%d").replace(tzinfo=utc)
+    day_start = datetime.datetime.strptime(options["date"], "%Y-%m-%d").replace(tzinfo=datetime.timezone.utc)
     day_end = day_start + datetime.timedelta(days=options["duration"])
 
     user_profile_query = UserProfile.objects.all()

analytics/management/commands/update_analytics_counts.py

@@ -2,12 +2,12 @@ import os
 import time
 from argparse import ArgumentParser
 from typing import Any, Dict
+from datetime import timezone
 
 from django.conf import settings
 from django.core.management.base import BaseCommand
 from django.utils.dateparse import parse_datetime
 from django.utils.timezone import now as timezone_now
-from django.utils.timezone import utc as timezone_utc
 
 from analytics.lib.counts import COUNT_STATS, logger, process_count_stat
 from scripts.lib.zulip_tools import ENDC, WARNING
@@ -60,11 +60,11 @@ class Command(BaseCommand):
 
         fill_to_time = parse_datetime(options['time'])
         if options['utc']:
-            fill_to_time = fill_to_time.replace(tzinfo=timezone_utc)
+            fill_to_time = fill_to_time.replace(tzinfo=timezone.utc)
         if fill_to_time.tzinfo is None:
             raise ValueError("--time must be timezone aware. Maybe you meant to use the --utc option?")
 
-        fill_to_time = floor_to_hour(fill_to_time.astimezone(timezone_utc))
+        fill_to_time = floor_to_hour(fill_to_time.astimezone(timezone.utc))
 
         if options['stat'] is not None:
             stats = [COUNT_STATS[options['stat']]]

analytics/tests/test_counts.py

@@ -1,4 +1,4 @@
-from datetime import datetime, timedelta
+from datetime import datetime, timedelta, timezone
 from typing import Any, Dict, List, Optional, Tuple, Type
 
 from unittest import mock
@@ -8,7 +8,6 @@ from django.db import models
 from django.db.models import Sum
 from django.test import TestCase
 from django.utils.timezone import now as timezone_now
-from django.utils.timezone import utc as timezone_utc
 
 from analytics.lib.counts import COUNT_STATS, CountStat, get_count_stats, \
     DependentCountStat, LoggingCountStat, do_aggregate_to_summary_table, \
@@ -33,7 +32,7 @@ class AnalyticsTestCase(TestCase):
     MINUTE = timedelta(seconds = 60)
     HOUR = MINUTE * 60
     DAY = HOUR * 24
-    TIME_ZERO = datetime(1988, 3, 14).replace(tzinfo=timezone_utc)
+    TIME_ZERO = datetime(1988, 3, 14, tzinfo=timezone.utc)
     TIME_LAST_HOUR = TIME_ZERO - HOUR
 
     def setUp(self) -> None:

analytics/tests/test_views.py

@@ -1,8 +1,7 @@
-from datetime import datetime, timedelta
+from datetime import datetime, timedelta, timezone
 from typing import List, Optional
 
 from unittest import mock
-from django.utils.timezone import utc
 from django.http import HttpResponse
 import ujson
 from django.utils.timezone import now as timezone_now
@@ -607,8 +606,8 @@ class TestGetChartDataHelpers(ZulipTestCase):
     # the only function that uses it at the moment
     def test_last_successful_fill(self) -> None:
         self.assertIsNone(last_successful_fill('non-existant'))
-        a_time = datetime(2016, 3, 14, 19).replace(tzinfo=utc)
+        a_time = datetime(2016, 3, 14, 19, tzinfo=timezone.utc)
-        one_hour_before = datetime(2016, 3, 14, 18).replace(tzinfo=utc)
+        one_hour_before = datetime(2016, 3, 14, 18, tzinfo=timezone.utc)
         fillstate = FillState.objects.create(property='property', end_time=a_time,
                                              state=FillState.DONE)
         self.assertEqual(last_successful_fill('property'), a_time)
@@ -631,9 +630,9 @@ class TestTimeRange(ZulipTestCase):
         HOUR = timedelta(hours=1)
         DAY = timedelta(days=1)
 
-        a_time = datetime(2016, 3, 14, 22, 59).replace(tzinfo=utc)
+        a_time = datetime(2016, 3, 14, 22, 59, tzinfo=timezone.utc)
-        floor_hour = datetime(2016, 3, 14, 22).replace(tzinfo=utc)
+        floor_hour = datetime(2016, 3, 14, 22, tzinfo=timezone.utc)
-        floor_day = datetime(2016, 3, 14).replace(tzinfo=utc)
+        floor_day = datetime(2016, 3, 14, tzinfo=timezone.utc)
 
         # test start == end
         self.assertEqual(time_range(a_time, a_time, CountStat.HOUR, None), [])

analytics/views.py

@@ -4,7 +4,7 @@ import re
 import time
 import urllib
 from collections import defaultdict
-from datetime import datetime, timedelta
+from datetime import datetime, timedelta, timezone
 from decimal import Decimal
 
 from typing import Any, Callable, Dict, List, \
@@ -18,7 +18,7 @@ from django.db.models.query import QuerySet
 from django.http import HttpRequest, HttpResponse, HttpResponseNotFound
 from django.shortcuts import render
 from django.template import loader
-from django.utils.timezone import now as timezone_now, utc as timezone_utc
+from django.utils.timezone import now as timezone_now
 from django.utils.translation import ugettext as _
 from django.utils.timesince import timesince
 from django.core.validators import URLValidator
@@ -253,7 +253,7 @@ def get_chart_data(request: HttpRequest, user_profile: UserProfile, chart_name:
                 start = realm.date_created
         if end is None:
             end = max(last_successful_fill(stat.property) or
-                      datetime.min.replace(tzinfo=timezone_utc) for stat in stats)
+                      datetime.min.replace(tzinfo=timezone.utc) for stat in stats)
 
         if start > end and (timezone_now() - start > MAX_TIME_FOR_FULL_ANALYTICS_GENERATION):
             logging.warning("User from realm %s attempted to access /stats, but the computed "

corporate/tests/test_stripe.py

@@ -1,4 +1,4 @@
-from datetime import datetime, timedelta
+from datetime import datetime, timedelta, timezone
 from decimal import Decimal
 from functools import wraps
 from unittest.mock import Mock, patch
@@ -14,7 +14,6 @@ import responses
 from django.core import signing
 from django.urls.resolvers import get_resolver
 from django.http import HttpResponse
-from django.utils.timezone import utc as timezone_utc
 from django.conf import settings
 from django.utils.timezone import now as timezone_now
 
@@ -265,9 +264,9 @@ class StripeTestCase(ZulipTestCase):
         self.signed_seat_count, self.salt = sign_string(str(self.seat_count))
         # Choosing dates with corresponding timestamps below 1500000000 so that they are
         # not caught by our timestamp normalization regex in normalize_fixture_data
-        self.now = datetime(2012, 1, 2, 3, 4, 5).replace(tzinfo=timezone_utc)
+        self.now = datetime(2012, 1, 2, 3, 4, 5, tzinfo=timezone.utc)
-        self.next_month = datetime(2012, 2, 2, 3, 4, 5).replace(tzinfo=timezone_utc)
+        self.next_month = datetime(2012, 2, 2, 3, 4, 5, tzinfo=timezone.utc)
-        self.next_year = datetime(2013, 1, 2, 3, 4, 5).replace(tzinfo=timezone_utc)
+        self.next_year = datetime(2013, 1, 2, 3, 4, 5, tzinfo=timezone.utc)
 
     def get_signed_seat_count_from_response(self, response: HttpResponse) -> Optional[str]:
         match = re.search(r'name=\"signed_seat_count\" value=\"(.+)\"', response.content.decode("utf-8"))
@@ -1552,24 +1551,24 @@ class RequiresBillingAccessTest(ZulipTestCase):
 
 class BillingHelpersTest(ZulipTestCase):
     def test_next_month(self) -> None:
-        anchor = datetime(2019, 12, 31, 1, 2, 3).replace(tzinfo=timezone_utc)
+        anchor = datetime(2019, 12, 31, 1, 2, 3, tzinfo=timezone.utc)
         period_boundaries = [
             anchor,
-            datetime(2020, 1, 31, 1, 2, 3).replace(tzinfo=timezone_utc),
+            datetime(2020, 1, 31, 1, 2, 3, tzinfo=timezone.utc),
             # Test that this is the 28th even during leap years
-            datetime(2020, 2, 28, 1, 2, 3).replace(tzinfo=timezone_utc),
+            datetime(2020, 2, 28, 1, 2, 3, tzinfo=timezone.utc),
-            datetime(2020, 3, 31, 1, 2, 3).replace(tzinfo=timezone_utc),
+            datetime(2020, 3, 31, 1, 2, 3, tzinfo=timezone.utc),
-            datetime(2020, 4, 30, 1, 2, 3).replace(tzinfo=timezone_utc),
+            datetime(2020, 4, 30, 1, 2, 3, tzinfo=timezone.utc),
-            datetime(2020, 5, 31, 1, 2, 3).replace(tzinfo=timezone_utc),
+            datetime(2020, 5, 31, 1, 2, 3, tzinfo=timezone.utc),
-            datetime(2020, 6, 30, 1, 2, 3).replace(tzinfo=timezone_utc),
+            datetime(2020, 6, 30, 1, 2, 3, tzinfo=timezone.utc),
-            datetime(2020, 7, 31, 1, 2, 3).replace(tzinfo=timezone_utc),
+            datetime(2020, 7, 31, 1, 2, 3, tzinfo=timezone.utc),
-            datetime(2020, 8, 31, 1, 2, 3).replace(tzinfo=timezone_utc),
+            datetime(2020, 8, 31, 1, 2, 3, tzinfo=timezone.utc),
-            datetime(2020, 9, 30, 1, 2, 3).replace(tzinfo=timezone_utc),
+            datetime(2020, 9, 30, 1, 2, 3, tzinfo=timezone.utc),
-            datetime(2020, 10, 31, 1, 2, 3).replace(tzinfo=timezone_utc),
+            datetime(2020, 10, 31, 1, 2, 3, tzinfo=timezone.utc),
-            datetime(2020, 11, 30, 1, 2, 3).replace(tzinfo=timezone_utc),
+            datetime(2020, 11, 30, 1, 2, 3, tzinfo=timezone.utc),
-            datetime(2020, 12, 31, 1, 2, 3).replace(tzinfo=timezone_utc),
+            datetime(2020, 12, 31, 1, 2, 3, tzinfo=timezone.utc),
-            datetime(2021, 1, 31, 1, 2, 3).replace(tzinfo=timezone_utc),
+            datetime(2021, 1, 31, 1, 2, 3, tzinfo=timezone.utc),
-            datetime(2021, 2, 28, 1, 2, 3).replace(tzinfo=timezone_utc)]
+            datetime(2021, 2, 28, 1, 2, 3, tzinfo=timezone.utc)]
         with self.assertRaises(AssertionError):
             add_months(anchor, -1)
         # Explicitly test add_months for each value of MAX_DAY_FOR_MONTH and
@@ -1586,9 +1585,9 @@ class BillingHelpersTest(ZulipTestCase):
 
     def test_compute_plan_parameters(self) -> None:
         # TODO: test rounding down microseconds
-        anchor = datetime(2019, 12, 31, 1, 2, 3).replace(tzinfo=timezone_utc)
+        anchor = datetime(2019, 12, 31, 1, 2, 3, tzinfo=timezone.utc)
-        month_later = datetime(2020, 1, 31, 1, 2, 3).replace(tzinfo=timezone_utc)
+        month_later = datetime(2020, 1, 31, 1, 2, 3, tzinfo=timezone.utc)
-        year_later = datetime(2020, 12, 31, 1, 2, 3).replace(tzinfo=timezone_utc)
+        year_later = datetime(2020, 12, 31, 1, 2, 3, tzinfo=timezone.utc)
         test_cases = [
             # TODO test with Decimal(85), not 85
             # TODO fix the mypy error by specifying the exact type

docs/contributing/code-style.md

@@ -153,19 +153,19 @@ Python allows datetime objects to not have an associated timezone, which can
 cause time-related bugs that are hard to catch with a test suite, or bugs
 that only show up during daylight savings time.
 
-Good ways to make timezone-aware datetimes are below. We import `timezone`
+Good ways to make timezone-aware datetimes are below. We import timezone
-functions as `from django.utils.timezone import now as timezone_now` and
+libraries as `from datetime import datetime, timezone` and `from
-`from django.utils.timezone import utc as timezone_utc`.
+django.utils.timezone import now as timezone_now`.
 
 Use:
 * `timezone_now()` to get a datetime when Django is available, such as
   in `zerver/`.
-* `datetime.now(tz=pytz.utc)` when Django is not available, such as
+* `datetime.now(tz=timezone.utc)` when Django is not available, such as
   for bots and scripts.
-* `datetime.fromtimestamp(timestamp, tz=timezone_utc)` if creating a
+* `datetime.fromtimestamp(timestamp, tz=timezone.utc)` if creating a
   datetime from a timestamp. This is also available as
   `zerver.lib.timestamp.timestamp_to_datetime`.
-* `datetime.strptime(date_string, format).replace(tzinfo=timezone_utc)` if
+* `datetime.strptime(date_string, format).replace(tzinfo=timezone.utc)` if
   creating a datetime from a formatted string that is in UTC.
 
 Idioms that result in timezone-naive datetimes, and should be avoided, are

puppet/zulip/files/nagios_plugins/zulip_postgres_common/check_postgres_backup

@@ -1,10 +1,9 @@
 #!/usr/bin/env python3
 
 import subprocess
-from datetime import datetime, timedelta
+from datetime import datetime, timedelta, timezone
 
 import dateutil.parser
-import pytz
 
 states = {
     "OK": 0,
@@ -28,7 +27,7 @@ try:
 except OSError:
     report('UNKNOWN', 'could not determine completion time of last Postgres backup')
 
-if datetime.now(tz=pytz.utc) - last_backup > timedelta(hours=25):
+if datetime.now(tz=timezone.utc) - last_backup > timedelta(hours=25):
     report('CRITICAL', 'last Postgres backup completed more than 25 hours ago: %s' % (last_backup,))
 
 report('OK', 'last Postgres backup completed less than 25 hours ago: %s' % (last_backup,))

puppet/zulip/files/postgresql/pg_backup_and_purge

@@ -7,9 +7,8 @@ import shlex
 import subprocess
 import logging
 import dateutil.parser
-import pytz
 import time
-from datetime import datetime, timedelta
+from datetime import datetime, timedelta, timezone
 from typing import Dict, List
 
 logging.Formatter.converter = time.gmtime
@@ -48,7 +47,7 @@ if len(pg_data_paths) != 1:
 pg_data_path = pg_data_paths[0]
 run(['env-wal-e', 'backup-push', pg_data_path])
 
-now = datetime.now(tz=pytz.utc)
+now = datetime.now(tz=timezone.utc)
 with open('/var/lib/nagios_state/last_postgres_backup', 'w') as f:
     f.write(now.isoformat())
     f.write("\n")

puppet/zulip/manifests/postgres_common.pp

@@ -15,10 +15,7 @@ class zulip::postgres_common {
         # Postgres Nagios check plugin
         'check-postgres',
         # Python modules used in our monitoring/worker threads
-        'python3-tz', # TODO: use a virtualenv instead
-        'python-tz', # TODO: use a virtualenv instead
         'python3-dateutil', # TODO: use a virtualenv instead
-        'python-dateutil', # TODO: use a virtualenv instead
       ]
       $postgres_user_reqs = [
         Package[$postgresql],
@@ -39,12 +36,8 @@ class zulip::postgres_common {
         # https://bucardo.org/check_postgres/
         # 'check-postgres',  # TODO
       ]
-      exec {'pip2_deps':
-        # Python modules used in our monitoring/worker threads
-        command => '/usr/bin/pip2 install pytz python-dateutil'
-      }
       exec {'pip3_deps':
-        command => 'python3 -m pip install pytz python-dateutil'
+        command => 'python3 -m pip install python-dateutil'
       }
       group { 'ssl-cert':
         ensure => present,

zerver/lib/digest.py

@@ -3,7 +3,6 @@ from typing import Any, Dict, List, Set, Tuple, Union
 from collections import defaultdict
 import datetime
 import logging
-import pytz
 
 from django.conf import settings
 from django.utils.timezone import now as timezone_now
@@ -168,7 +167,7 @@ def handle_digest_email(user_profile_id: int, cutoff: float,
     user_profile = get_user_profile_by_id(user_profile_id)
 
     # Convert from epoch seconds to a datetime object.
-    cutoff_date = datetime.datetime.fromtimestamp(int(cutoff), tz=pytz.utc)
+    cutoff_date = datetime.datetime.fromtimestamp(int(cutoff), tz=datetime.timezone.utc)
 
     context = common_context(user_profile)
 

zerver/lib/import_realm.py

@@ -9,7 +9,7 @@ from bs4 import BeautifulSoup
 from django.conf import settings
 from django.db import connection
 from django.db.models import Max
-from django.utils.timezone import utc as timezone_utc, now as timezone_now
+from django.utils.timezone import now as timezone_now
 from typing import Any, Dict, List, Optional, Set, Tuple, \
     Iterable, cast
 
@@ -109,7 +109,7 @@ def fix_datetime_fields(data: TableData, table: TableName) -> None:
     for item in data[table]:
         for field_name in DATE_FIELDS[table]:
             if item[field_name] is not None:
-                item[field_name] = datetime.datetime.fromtimestamp(item[field_name], tz=timezone_utc)
+                item[field_name] = datetime.datetime.fromtimestamp(item[field_name], tz=datetime.timezone.utc)
 
 def fix_upload_links(data: TableData, message_table: TableName) -> None:
     """

zerver/lib/logging_util.py

@@ -1,14 +1,13 @@
 # System documented in https://zulip.readthedocs.io/en/latest/subsystems/logging.html
 
 from django.utils.timezone import now as timezone_now
-from django.utils.timezone import utc as timezone_utc
 
 import hashlib
 import logging
 import threading
 import traceback
 from typing import Optional, Tuple
-from datetime import datetime, timedelta
+from datetime import datetime, timedelta, timezone
 from django.conf import settings
 from django.core.cache import cache
 from logging import Logger
@@ -28,7 +27,7 @@ class _RateLimitFilter:
     Adapted from https://djangosnippets.org/snippets/2242/.
 
     """
-    last_error = datetime.min.replace(tzinfo=timezone_utc)
+    last_error = datetime.min.replace(tzinfo=timezone.utc)
     # This thread-local variable is used to detect recursive
     # exceptions during exception handling (primarily intended for
     # when accessing the shared cache throws an exception).

zerver/lib/timestamp.py

@@ -1,28 +1,25 @@
 import datetime
 import calendar
-from django.utils.timezone import utc as timezone_utc
 
 class TimezoneNotUTCException(Exception):
     pass
 
 def verify_UTC(dt: datetime.datetime) -> None:
-    if dt.tzinfo is None or dt.tzinfo.utcoffset(dt) != timezone_utc.utcoffset(dt):
+    if dt.tzinfo is None or dt.tzinfo.utcoffset(dt) != datetime.timezone.utc.utcoffset(dt):
         raise TimezoneNotUTCException("Datetime %s does not have a UTC timezone." % (dt,))
 
 def convert_to_UTC(dt: datetime.datetime) -> datetime.datetime:
     if dt.tzinfo is None:
-        return dt.replace(tzinfo=timezone_utc)
+        return dt.replace(tzinfo=datetime.timezone.utc)
-    return dt.astimezone(timezone_utc)
+    return dt.astimezone(datetime.timezone.utc)
 
 def floor_to_hour(dt: datetime.datetime) -> datetime.datetime:
     verify_UTC(dt)
-    return datetime.datetime(*dt.timetuple()[:4]) \
+    return datetime.datetime(*dt.timetuple()[:4], tzinfo=datetime.timezone.utc)
-                   .replace(tzinfo=timezone_utc)
 
 def floor_to_day(dt: datetime.datetime) -> datetime.datetime:
     verify_UTC(dt)
-    return datetime.datetime(*dt.timetuple()[:3]) \
+    return datetime.datetime(*dt.timetuple()[:3], tzinfo=datetime.timezone.utc)
-                   .replace(tzinfo=timezone_utc)
 
 def ceiling_to_hour(dt: datetime.datetime) -> datetime.datetime:
     floor = floor_to_hour(dt)
@@ -37,7 +34,7 @@ def ceiling_to_day(dt: datetime.datetime) -> datetime.datetime:
     return floor + datetime.timedelta(days=1)
 
 def timestamp_to_datetime(timestamp: float) -> datetime.datetime:
-    return datetime.datetime.fromtimestamp(float(timestamp), tz=timezone_utc)
+    return datetime.datetime.fromtimestamp(float(timestamp), tz=datetime.timezone.utc)
 
 def datetime_to_timestamp(dt: datetime.datetime) -> int:
     verify_UTC(dt)

zerver/management/commands/dump_messages.py

@@ -3,7 +3,6 @@ import time
 from typing import Any
 
 from django.core.management.base import CommandParser
-from django.utils.timezone import utc as timezone_utc
 
 from zerver.lib.management import ZulipBaseCommand
 from zerver.models import Message, Recipient, Stream
@@ -26,7 +25,7 @@ class Command(ZulipBaseCommand):
         streams = Stream.objects.filter(realm=realm, invite_only=False)
         recipients = Recipient.objects.filter(
             type=Recipient.STREAM, type_id__in=[stream.id for stream in streams])
-        cutoff = datetime.datetime.fromtimestamp(options["since"], tz=timezone_utc)
+        cutoff = datetime.datetime.fromtimestamp(options["since"], tz=datetime.timezone.utc)
         messages = Message.objects.filter(date_sent__gt=cutoff, recipient__in=recipients)
 
         for message in messages:

zerver/tests/test_push_notifications.py

@@ -17,7 +17,6 @@ from django.http import HttpResponse
 from django.db import transaction
 from django.db.models import F
 from django.utils.crypto import get_random_string
-from django.utils.timezone import utc as timezone_utc
 
 from analytics.lib.counts import CountStat, LoggingCountStat
 from analytics.models import InstallationCount, RealmCount
@@ -383,7 +382,7 @@ class PushBouncerNotificationTest(BouncerTestCase):
         self.assertEqual(len(tokens), 0)
 
 class AnalyticsBouncerTest(BouncerTestCase):
-    TIME_ZERO = datetime.datetime(1988, 3, 14).replace(tzinfo=timezone_utc)
+    TIME_ZERO = datetime.datetime(1988, 3, 14, tzinfo=datetime.timezone.utc)
 
     @override_settings(PUSH_NOTIFICATION_BOUNCER_URL='https://push.zulip.org.example.com')
     @mock.patch('zerver.lib.remote_server.requests.request')

zerver/tests/test_signup.py

@@ -81,7 +81,6 @@ import ujson
 from typing import Any, List, Optional
 
 import urllib
-import pytz
 
 class RedirectAndLogIntoSubdomainTestCase(ZulipTestCase):
     def test_data(self) -> None:
@@ -4087,22 +4086,22 @@ class FollowupEmailTest(ZulipTestCase):
     def test_followup_day2_email(self) -> None:
         user_profile = self.example_user('hamlet')
         # Test date_joined == Sunday
-        user_profile.date_joined = datetime.datetime(2018, 1, 7, 1, 0, 0, 0, pytz.UTC)
+        user_profile.date_joined = datetime.datetime(2018, 1, 7, 1, 0, 0, 0, tzinfo=datetime.timezone.utc)
         self.assertEqual(followup_day2_email_delay(user_profile), datetime.timedelta(days=2, hours=-1))
         # Test date_joined == Tuesday
-        user_profile.date_joined = datetime.datetime(2018, 1, 2, 1, 0, 0, 0, pytz.UTC)
+        user_profile.date_joined = datetime.datetime(2018, 1, 2, 1, 0, 0, 0, tzinfo=datetime.timezone.utc)
         self.assertEqual(followup_day2_email_delay(user_profile), datetime.timedelta(days=2, hours=-1))
         # Test date_joined == Thursday
-        user_profile.date_joined = datetime.datetime(2018, 1, 4, 1, 0, 0, 0, pytz.UTC)
+        user_profile.date_joined = datetime.datetime(2018, 1, 4, 1, 0, 0, 0, tzinfo=datetime.timezone.utc)
         self.assertEqual(followup_day2_email_delay(user_profile), datetime.timedelta(days=1, hours=-1))
         # Test date_joined == Friday
-        user_profile.date_joined = datetime.datetime(2018, 1, 5, 1, 0, 0, 0, pytz.UTC)
+        user_profile.date_joined = datetime.datetime(2018, 1, 5, 1, 0, 0, 0, tzinfo=datetime.timezone.utc)
         self.assertEqual(followup_day2_email_delay(user_profile), datetime.timedelta(days=3, hours=-1))
 
         # Time offset of America/Phoenix is -07:00
         user_profile.timezone = 'America/Phoenix'
         # Test date_joined == Friday in UTC, but Thursday in the user's timezone
-        user_profile.date_joined = datetime.datetime(2018, 1, 5, 1, 0, 0, 0, pytz.UTC)
+        user_profile.date_joined = datetime.datetime(2018, 1, 5, 1, 0, 0, 0, tzinfo=datetime.timezone.utc)
         self.assertEqual(followup_day2_email_delay(user_profile), datetime.timedelta(days=1, hours=-1))
 
 class NoReplyEmailTest(ZulipTestCase):

zerver/tests/test_timestamp.py

@@ -1,21 +1,17 @@
-from django.utils.timezone import utc as timezone_utc
-
 from zerver.lib.test_classes import ZulipTestCase
 from zerver.lib.timestamp import floor_to_hour, floor_to_day, ceiling_to_hour, \
     timestamp_to_datetime, datetime_to_timestamp, \
     TimezoneNotUTCException, convert_to_UTC
 
-from datetime import timedelta
+from datetime import timedelta, timezone
 from dateutil import parser
-import pytz
 
 class TestTimestamp(ZulipTestCase):
     def test_datetime_and_timestamp_conversions(self) -> None:
         timestamp = 1483228800
         for dt in [
                 parser.parse('2017-01-01 00:00:00.123 UTC'),
-                parser.parse('2017-01-01 00:00:00.123').replace(tzinfo=timezone_utc),
+                parser.parse('2017-01-01 00:00:00.123').replace(tzinfo=timezone.utc)]:
-                parser.parse('2017-01-01 00:00:00.123').replace(tzinfo=pytz.utc)]:
             self.assertEqual(timestamp_to_datetime(timestamp), dt-timedelta(microseconds=123000))
             self.assertEqual(datetime_to_timestamp(dt), timestamp)
 
@@ -28,7 +24,7 @@ class TestTimestamp(ZulipTestCase):
     def test_convert_to_UTC(self) -> None:
         utc_datetime = parser.parse('2017-01-01 00:00:00.123 UTC')
         for dt in [
-                parser.parse('2017-01-01 00:00:00.123').replace(tzinfo=timezone_utc),
+                parser.parse('2017-01-01 00:00:00.123').replace(tzinfo=timezone.utc),
                 parser.parse('2017-01-01 00:00:00.123'),
                 parser.parse('2017-01-01 05:00:00.123+05')]:
             self.assertEqual(convert_to_UTC(dt), utc_datetime)

zerver/webhooks/librato/view.py

@@ -1,9 +1,8 @@
-from datetime import datetime
+from datetime import datetime, timezone
 from typing import Any, Callable, Dict, List, Tuple
 
 import ujson
 from django.http import HttpRequest, HttpResponse
-from django.utils.timezone import utc as timezone_utc
 from django.utils.translation import ugettext as _
 
 from zerver.decorator import api_key_only_webhook_view
@@ -41,7 +40,7 @@ class LibratoWebhookParser:
     def parse_violation(self, violation: Dict[str, Any]) -> Tuple[str, str]:
         metric_name = violation['metric']
         recorded_at = datetime.fromtimestamp((violation['recorded_at']),
-                                             tz=timezone_utc).strftime('%Y-%m-%d %H:%M:%S')
+                                             tz=timezone.utc).strftime('%Y-%m-%d %H:%M:%S')
         return metric_name, recorded_at
 
     def parse_conditions(self) -> List[Dict[str, Any]]:
@@ -90,7 +89,7 @@ class LibratoWebhookHandler(LibratoWebhookParser):
     def handle_alert_clear_message(self) -> str:
         alert_clear_template = "Alert [alert_name]({alert_url}) has cleared at {trigger_time} UTC!"
         trigger_time = datetime.fromtimestamp((self.payload['trigger_time']),
-                                              tz=timezone_utc).strftime('%Y-%m-%d %H:%M:%S')
+                                              tz=timezone.utc).strftime('%Y-%m-%d %H:%M:%S')
         alert_id, alert_name, alert_url, alert_runbook_url = self.parse_alert()
         content = alert_clear_template.format(alert_name=alert_name,
                                               alert_url=alert_url,

zilencer/views.py

@@ -7,7 +7,6 @@ from django.core.validators import validate_email, URLValidator
 from django.db import IntegrityError, transaction
 from django.http import HttpRequest, HttpResponse
 from django.utils import timezone
-from django.utils.timezone import utc as timezone_utc
 from django.utils.translation import ugettext as _, ugettext as err_
 from django.views.decorators.csrf import csrf_exempt
 
@@ -224,7 +223,7 @@ def remote_server_post_analytics(request: HttpRequest,
         realm_id=row['realm'],
         remote_id=row['id'],
         server=server,
-        end_time=datetime.datetime.fromtimestamp(row['end_time'], tz=timezone_utc),
+        end_time=datetime.datetime.fromtimestamp(row['end_time'], tz=datetime.timezone.utc),
         subgroup=row['subgroup'],
         value=row['value']) for row in realm_counts]
     batch_create_table_data(server, RemoteRealmCount, row_objects)
@@ -233,7 +232,7 @@ def remote_server_post_analytics(request: HttpRequest,
         property=row['property'],
         remote_id=row['id'],
         server=server,
-        end_time=datetime.datetime.fromtimestamp(row['end_time'], tz=timezone_utc),
+        end_time=datetime.datetime.fromtimestamp(row['end_time'], tz=datetime.timezone.utc),
         subgroup=row['subgroup'],
         value=row['value']) for row in installation_counts]
     batch_create_table_data(server, RemoteInstallationCount, row_objects)
@@ -243,7 +242,7 @@ def remote_server_post_analytics(request: HttpRequest,
             realm_id=row['realm'],
             remote_id=row['id'],
             server=server,
-            event_time=datetime.datetime.fromtimestamp(row['event_time'], tz=timezone_utc),
+            event_time=datetime.datetime.fromtimestamp(row['event_time'], tz=datetime.timezone.utc),
             backfilled=row['backfilled'],
             extra_data=row['extra_data'],
             event_type=row['event_type']) for row in realmauditlog_rows]