From 7c31e195db963ad1ebb28265e721097000fa84d1 Mon Sep 17 00:00:00 2001
From: Aymeric Augustin <aymeric.augustin@m4x.org>
Date: Sat, 7 Sep 2013 18:56:49 -0500
Subject: [PATCH] [1.6.x] Fixed #18766 -- Pointed to pytz when LocalTimezone
 fails.

Thanks void for the report.

Backport of ded11aa6 from master.
---
 django/utils/timezone.py           | 25 +++++++++++++++++++++++--
 tests/utils_tests/test_timezone.py |  7 +++++++
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/django/utils/timezone.py b/django/utils/timezone.py
index 3493e056fb3..93ef4dfd57f 100644
--- a/django/utils/timezone.py
+++ b/django/utils/timezone.py
@@ -1,10 +1,12 @@
-"""Timezone helper functions.
+"""
+Timezone-related classes and functions.
 
 This module uses pytz when it's available and fallbacks when it isn't.
 """
 
 from datetime import datetime, timedelta, tzinfo
 from threading import local
+import sys
 import time as _time
 
 try:
@@ -45,12 +47,14 @@ class UTC(tzinfo):
     def dst(self, dt):
         return ZERO
 
-class LocalTimezone(tzinfo):
+class ReferenceLocalTimezone(tzinfo):
     """
     Local time implementation taken from Python's docs.
 
     Used only when pytz isn't available, and most likely inaccurate. If you're
     having trouble with this class, don't waste your time, just install pytz.
+
+    Kept identical to the reference version. Subclasses contain improvements.
     """
 
     def __init__(self):
@@ -91,6 +95,23 @@ class LocalTimezone(tzinfo):
         tt = _time.localtime(stamp)
         return tt.tm_isdst > 0
 
+class LocalTimezone(ReferenceLocalTimezone):
+    """
+    Slightly improved local time implementation focusing on correctness.
+
+    It still crashes on dates before 1970 or after 2038, but at least the
+    error message is helpful.
+    """
+
+    def _isdst(self, dt):
+        try:
+            return super(LocalTimezone, self)._isdst(dt)
+        except (OverflowError, ValueError) as exc:
+            exc_type = type(exc)
+            exc_value = exc_type(
+                    "Unsupported value: %r. You should install pytz." % dt)
+            exc_value.__cause__ = exc
+            six.reraise(exc_type, exc_value, sys.exc_info()[2])
 
 utc = pytz.utc if pytz else UTC()
 """UTC time zone as a tzinfo instance."""
diff --git a/tests/utils_tests/test_timezone.py b/tests/utils_tests/test_timezone.py
index 650198e8ffe..86e3a66008b 100644
--- a/tests/utils_tests/test_timezone.py
+++ b/tests/utils_tests/test_timezone.py
@@ -2,6 +2,7 @@ import copy
 import datetime
 import pickle
 from django.test.utils import override_settings
+from django.utils import six
 from django.utils import timezone
 from django.utils.tzinfo import FixedOffset
 from django.utils import unittest
@@ -19,6 +20,12 @@ class TimezoneTests(unittest.TestCase):
         local_now = timezone.localtime(now, local_tz)
         self.assertEqual(local_now.tzinfo, local_tz)
 
+    def test_localtime_out_of_range(self):
+        local_tz = timezone.LocalTimezone()
+        long_ago = datetime.datetime(1900, 1, 1, tzinfo=timezone.utc)
+        with six.assertRaisesRegex(self, OverflowError, "install pytz"):
+            timezone.localtime(long_ago, local_tz)
+
     def test_now(self):
         with override_settings(USE_TZ=True):
             self.assertTrue(timezone.is_aware(timezone.now()))