Fixed #27327 -- Simplified time zone handling by requiring pytz.

django/db/backends/base/base.py

@@ -4,6 +4,8 @@
 from collections import deque
 from contextlib import contextmanager
 
+import pytz
+
 from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured
 from django.db import DEFAULT_DB_ALIAS
@@ -16,11 +18,6 @@
 from django.utils.functional import cached_property
 from django.utils.six.moves import _thread as thread
 
-try:
-    import pytz
-except ImportError:
-    pytz = None
-
 NO_DB_ALIAS = '__no_db__'
 
 
@@ -128,7 +125,6 @@ def timezone(self):
         elif self.settings_dict['TIME_ZONE'] is None:
             return timezone.utc
         else:
-            # Only this branch requires pytz.
             return pytz.timezone(self.settings_dict['TIME_ZONE'])
 
     @cached_property
@@ -207,10 +203,6 @@ def check_settings(self):
                 raise ImproperlyConfigured(
                     "Connection '%s' cannot set TIME_ZONE because its engine "
                     "handles time zones conversions natively." % self.alias)
-            elif pytz is None:
-                raise ImproperlyConfigured(
-                    "Connection '%s' cannot set TIME_ZONE because pytz isn't "
-                    "installed." % self.alias)
 
     def ensure_connection(self):
         """

django/db/backends/mysql/features.py

@@ -3,11 +3,6 @@
 
 from .base import Database
 
-try:
-    import pytz
-except ImportError:
-    pytz = None
-
 
 class DatabaseFeatures(BaseDatabaseFeatures):
     empty_fetchmany_value = ()
@@ -56,14 +51,6 @@ def supports_microsecond_precision(self):
 
     @cached_property
     def has_zoneinfo_database(self):
-        # MySQL accepts full time zones names (eg. Africa/Nairobi) but rejects
-        # abbreviations (eg. EAT). When pytz isn't installed and the current
-        # time zone is LocalTimezone (the only sensible value in this
-        # context), the current time zone name will be an abbreviation. As a
-        # consequence, MySQL cannot perform time zone conversions reliably.
-        if pytz is None:
-            return False
-
         # Test if the time zone definitions are installed.
         with self.connection.cursor() as cursor:
             cursor.execute("SELECT 1 FROM mysql.time_zone LIMIT 1")

django/db/backends/oracle/features.py

@@ -1,11 +1,6 @@
 from django.db.backends.base.features import BaseDatabaseFeatures
 from django.db.utils import InterfaceError
 
-try:
-    import pytz
-except ImportError:
-    pytz = None
-
 
 class DatabaseFeatures(BaseDatabaseFeatures):
     empty_fetchmany_value = ()
@@ -19,7 +14,6 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_subqueries_in_group_by = False
     supports_transactions = True
     supports_timezones = False
-    has_zoneinfo_database = pytz is not None
     supports_bitwise_or = False
     has_native_duration_field = True
     can_defer_constraint_checks = True

django/db/backends/sqlite3/base.py

@@ -11,6 +11,8 @@
 import re
 import warnings
 
+import pytz
+
 from django.conf import settings
 from django.db import utils
 from django.db.backends import utils as backend_utils
@@ -23,11 +25,6 @@
 from django.utils.encoding import force_text
 from django.utils.safestring import SafeBytes
 
-try:
-    import pytz
-except ImportError:
-    pytz = None
-
 try:
     try:
         from pysqlite2 import dbapi2 as Database

django/db/backends/sqlite3/features.py

@@ -7,11 +7,6 @@
 
 from .base import Database
 
-try:
-    import pytz
-except ImportError:
-    pytz = None
-
 
 class DatabaseFeatures(BaseDatabaseFeatures):
     # SQLite cannot handle us only partially reading from a cursor's result set
@@ -78,7 +73,3 @@ def supports_stddev(self):
                 has_support = False
             cursor.execute('DROP TABLE STDDEV_TEST')
         return has_support
-
-    @cached_property
-    def has_zoneinfo_database(self):
-        return pytz is not None

django/db/backends/sqlite3/operations.py

@@ -4,7 +4,7 @@
 import uuid
 
 from django.conf import settings
-from django.core.exceptions import FieldError, ImproperlyConfigured
+from django.core.exceptions import FieldError
 from django.db import utils
 from django.db.backends import utils as backend_utils
 from django.db.backends.base.operations import BaseDatabaseOperations
@@ -13,11 +13,6 @@
 from django.utils.dateparse import parse_date, parse_datetime, parse_time
 from django.utils.duration import duration_string
 
-try:
-    import pytz
-except ImportError:
-    pytz = None
-
 
 class DatabaseOperations(BaseDatabaseOperations):
     def bulk_batch_size(self, fields, objs):
@@ -77,27 +72,19 @@ def time_trunc_sql(self, lookup_type, field_name):
         # cause a collision with a field name).
         return "django_time_trunc('%s', %s)" % (lookup_type.lower(), field_name)
 
-    def _require_pytz(self):
-        if settings.USE_TZ and pytz is None:
-            raise ImproperlyConfigured("This query requires pytz, but it isn't installed.")
-
     def datetime_cast_date_sql(self, field_name, tzname):
-        self._require_pytz()
         return "django_datetime_cast_date(%s, %%s)" % field_name, [tzname]
 
     def datetime_cast_time_sql(self, field_name, tzname):
-        self._require_pytz()
         return "django_datetime_cast_time(%s, %%s)" % field_name, [tzname]
 
     def datetime_extract_sql(self, lookup_type, field_name, tzname):
         # Same comment as in date_extract_sql.
-        self._require_pytz()
         return "django_datetime_extract('%s', %s, %%s)" % (
             lookup_type.lower(), field_name), [tzname]
 
     def datetime_trunc_sql(self, lookup_type, field_name, tzname):
         # Same comment as in date_trunc_sql.
-        self._require_pytz()
         return "django_datetime_trunc('%s', %s, %%s)" % (
             lookup_type.lower(), field_name), [tzname]
 

django/db/models/functions/datetime.py

@@ -191,7 +191,7 @@ def convert_value(self, value, expression, connection, context):
                 if value is None:
                     raise ValueError(
                         "Database returned an invalid datetime value. "
-                        "Are time zone definitions for your database and pytz installed?"
+                        "Are time zone definitions for your database installed?"
                     )
                 value = value.replace(tzinfo=None)
                 value = timezone.make_aware(value, self.tzinfo)

django/templatetags/tz.py

@@ -1,14 +1,10 @@
 from datetime import datetime, tzinfo
 
+import pytz
+
 from django.template import Library, Node, TemplateSyntaxError
 from django.utils import six, timezone
 
-try:
-    import pytz
-except ImportError:
-    pytz = None
-
-
 register = Library()
 
 
@@ -44,7 +40,6 @@ def do_timezone(value, arg):
     Converts a datetime to local time in a given time zone.
 
     The argument must be an instance of a tzinfo subclass or a time zone name.
-    If it is a time zone name, pytz is required.
 
     Naive datetimes are assumed to be in local time in the default time zone.
     """
@@ -64,7 +59,7 @@ def do_timezone(value, arg):
     # Obtain a tzinfo instance
     if isinstance(arg, tzinfo):
         tz = arg
-    elif isinstance(arg, six.string_types) and pytz is not None:
+    elif isinstance(arg, six.string_types):
         try:
             tz = pytz.timezone(arg)
         except pytz.UnknownTimeZoneError:
@@ -156,8 +151,8 @@ def timezone_tag(parser, token):
     Enables a given time zone just for this block.
 
     The ``timezone`` argument must be an instance of a ``tzinfo`` subclass, a
-    time zone name, or ``None``. If is it a time zone name, pytz is required.
-    If it is ``None``, the default time zone is used within the block.
+    time zone name, or ``None``. If it is ``None``, the default time zone is
+    used within the block.
 
     Sample usage::