{"schema_version":"4.0","kind":"technical_task_solution","page":{"title":"How do you add is_dst handling to Django Trunc to avoid AmbiguousTimeError and NonExistentTimeError?","url":"https://agent-solution.dev/tasks/django-pytz-exceptions-ambiguoustimeerror-trunc","manifest_url":"https://agent-solution.dev/tasks/django-pytz-exceptions-ambiguoustimeerror-trunc/agent.json","description":"django/django — pytz.exceptions.AmbiguousTimeError in Trunc. Traceback path: django/db/models/functions/datetime.py.","updated_at":"2026-08-27"},"task_match":{"technology":"django/django","error_signature":"pytz.exceptions.AmbiguousTimeError","focus_symbol":"Trunc","focus_path":"django/db/models/functions/datetime.py","problem_class":"python-traceback-repairs","statement_kind":"verbatim agent-facing issue statement","task_statement":"Trunc() should allow passing is_dst resolution to avoid NonExistentTimeError/AmbiguousTimeError\nDescription\n\t \n\t\t(last modified by Alexander Holmbäck)\n\t \nWhen Trunc() truncates to a nonexisting or ambiguous datetime, the exception raised by pytz remains unhandled. The expected behavior would, IMO, be to not check the validity of truncated dates.\nThis test for example:\nimport datetime\nimport pytz\nfrom django.db.models.functions import Trunc\nfrom django.test import TestCase\nfrom django.utils import timezone\nfrom .models import Log\nclass TestTruncateToInvalidTime(TestCase):\n\tdef test_truncate_to_dst_ends_stockholm(self):\n\t\ttzinfo = pytz.timezone('Europe/Stockholm')\n\t\ttimestamp = datetime.datetime(2018, 10, 28, 2, tzinfo=tzinfo)\n\t\tLog.objects.create(timestamp=timestamp)\n\t\tlogs = Log.objects.annotate(day=Trunc('timestamp', 'hour')).all()\n\t\ttimezone.activate(tzinfo)\n\t\tself.assertEqual(logs[0].day.day, 28)\nResults in the following error:\n======================================================================\nERROR: test_truncate_to_dst_ends_stockholm (trunc.tests.TestTruncateInvalidTime)\n----------------------------------------------------------------------\nTraceback (most recent call last):\n File \"/home/alex/tickets/trunc/tests.py\", line 47, in test_truncate_to_dst_ends_stockholm\n\tself.assertEqual(logs[0].day.day, 28)\n File \"/home/alex/django/django/db/models/query.py\", line 303, in __getitem__\n\tqs._fetch_all()\n File \"/home/alex/django/django/db/models/query.py\", line 1190, in _fetch_all\n\tself._result_cache = list(self._iterable_class(self))\n File \"/home/alex/django/django/db/models/query.py\", line 64, in __iter__\n\tfor row in compiler.results_iter(results):\n File \"/home/alex/django/django/db/models/sql/compiler.py\", line 1013, in apply_converters\n\tvalue = converter(value, expression, connection)\n File \"/home/alex/django/django/db/models/functions/datetime.py\", line 225, in convert_value\n\tvalue = timezone.make_aware(value, self.tzinfo)\n File \"/home/alex/django/django/utils/timezone.py\", line 270, in make_aware\n\treturn timezone.localize(value, is_dst=is_dst)\n File \"/home/alex/.virtualenvs/djangodev/lib/python3.6/site-packages/pytz/tzinfo.py\", line 363, in localize\n\traise AmbiguousTimeError(dt)\npytz.exceptions.AmbiguousTimeError: 2018-10-28 02:00:00","technical_objective":"Give callers of Django's database date/time truncation functions a way to control how an ambiguous or non-existent local datetime is resolved when the truncated value is converted back to an aware datetime. The deliverable is a change to the Trunc-family database functions (and whatever timezone helper they rely on) so that truncation to a DST transition boundary no longer surfaces an unhandled pytz exception to the ORM caller.","success_condition":"a queryset annotation that truncates a timestamp onto a non-existent or ambiguous local time can be evaluated without raising, with the resolution behaviour selectable by the caller; existing Trunc results for unambiguous datetimes and the current default behaviour of the timezone helpers stay intact.","upstream_source":{"repository":"django/django","commit":"4c086d7da4c5cf23935a5340dbb9a8d6835cf7cc","version":"3.0"},"primary_terms":["pytz.exceptions.AmbiguousTimeError","Trunc","django/db/models/functions/datetime.py","django/django","TruncBase","convert_value","is_dst","make_aware","timezone.localize","apply_converters","from django.db.models.functions import Trunc","from django.utils import timezone"],"search_signals":["Error signature: pytz.exceptions.AmbiguousTimeError","Traceback path: django/db/models/functions/datetime.py","Repository: django/django","Issue title: Trunc() should allow passing is_dst resolution to avoid NonExistentTimeError/AmbiguousTimeError.","Symbols: Trunc, TruncBase, convert_value, is_dst, make_aware, timezone.localize, apply_converters.","Imports: from django.db.models.functions import Trunc, from django.utils import timezone.","Files: django/db/models/functions/datetime.py, django/utils/timezone.py, django/db/models/sql/compiler.py, django/db/models/query.py.","Exceptions: pytz.exceptions.AmbiguousTimeError, NonExistentTimeError.","Verbatim strings: pytz.exceptions.AmbiguousTimeError: 2018-10-28 02:00:00, ERROR: test_truncate_to_dst_ends_stockholm (trunc.tests.TestTruncateInvalidTime).","Technologies: Django ORM annotations, pytz, DST transitions, Europe/Stockholm."],"match_summary":"Matches django/django work keyed on pytz.exceptions.AmbiguousTimeError in Trunc.","demonstrations":null},"evidence_search":{"guide_url":"https://agent-solution.dev/tasks/django-pytz-exceptions-ambiguoustimeerror-trunc/llms.txt","method":"GET","url":"https://agent-solution.dev/tasks/django-pytz-exceptions-ambiguoustimeerror-trunc/search","url_template":"https://agent-solution.dev/tasks/django-pytz-exceptions-ambiguoustimeerror-trunc/search?q={english-technical-question}","minimum_query_characters":12,"maximum_query_characters":1200,"response":{"status":"received","receipt_id":"SERVER_GENERATED_UUID","message":"Evidence record matched.","evidence_record":{"title":"How do you add is_dst handling to Django Trunc to avoid AmbiguousTimeError and NonExistentTimeError?","summary":"Matches django/django work keyed on pytz.exceptions.AmbiguousTimeError in Trunc.","task_statement":"Trunc() should allow passing is_dst resolution to avoid NonExistentTimeError/AmbiguousTimeError\nDescription\n\t \n\t\t(last modified by Alexander Holmbäck)\n\t \nWhen Trunc() truncates to a nonexisting or ambiguous datetime, the exception raised by pytz remains unhandled. The expected behavior would, IMO, be to not check the validity of truncated dates.\nThis test for example:\nimport datetime\nimport pytz\nfrom django.db.models.functions import Trunc\nfrom django.test import TestCase\nfrom django.utils import timezone\nfrom .models import Log\nclass TestTruncateToInvalidTime(TestCase):\n\tdef test_truncate_to_dst_ends_stockholm(self):\n\t\ttzinfo = pytz.timezone('Europe/Stockholm')\n\t\ttimestamp = datetime.datetime(2018, 10, 28, 2, tzinfo=tzinfo)\n\t\tLog.objects.create(timestamp=timestamp)\n\t\tlogs = Log.objects.annotate(day=Trunc('timestamp', 'hour')).all()\n\t\ttimezone.activate(tzinfo)\n\t\tself.assertEqual(logs[0].day.day, 28)\nResults in the following error:\n======================================================================\nERROR: test_truncate_to_dst_ends_stockholm (trunc.tests.TestTruncateInvalidTime)\n----------------------------------------------------------------------\nTraceback (most recent call last):\n File \"/home/alex/tickets/trunc/tests.py\", line 47, in test_truncate_to_dst_ends_stockholm\n\tself.assertEqual(logs[0].day.day, 28)\n File \"/home/alex/django/django/db/models/query.py\", line 303, in __getitem__\n\tqs._fetch_all()\n File \"/home/alex/django/django/db/models/query.py\", line 1190, in _fetch_all\n\tself._result_cache = list(self._iterable_class(self))\n File \"/home/alex/django/django/db/models/query.py\", line 64, in __iter__\n\tfor row in compiler.results_iter(results):\n File \"/home/alex/django/django/db/models/sql/compiler.py\", line 1013, in apply_converters\n\tvalue = converter(value, expression, connection)\n File \"/home/alex/django/django/db/models/functions/datetime.py\", line 225, in convert_value\n\tvalue = timezone.make_aware(value, self.tzinfo)\n File \"/home/alex/django/django/utils/timezone.py\", line 270, in make_aware\n\treturn timezone.localize(value, is_dst=is_dst)\n File \"/home/alex/.virtualenvs/djangodev/lib/python3.6/site-packages/pytz/tzinfo.py\", line 363, in localize\n\traise AmbiguousTimeError(dt)\npytz.exceptions.AmbiguousTimeError: 2018-10-28 02:00:00","technical_objective":"Give callers of Django's database date/time truncation functions a way to control how an ambiguous or non-existent local datetime is resolved when the truncated value is converted back to an aware datetime. 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