Raise when unable to detect name of local timezone (#3576)

When `tzlocal` is unable to detect the name of the local timezone, it
labels it as 'local', which is not understood by django. When this
happens, ask the user to set the desired timezone using the TZ
environment variable.

aiida/backends/djsite/settings.py

@@ -68,7 +68,9 @@
 # http://www.i18nguy.com/unicode/language-identifiers.html
 LANGUAGE_CODE = 'en-us'
 
-# Local time zone for this installation. Always choose the system timezone
+# Local time zone for this installation. Always choose the system timezone.
+# Note: This causes django to set the 'TZ' environment variable, which is read by tzlocal from then onwards.
+# See https://docs.djangoproject.com/en/2.2/ref/settings/#std:setting-TIME_ZONE
 TIME_ZONE = get_current_timezone().zone
 
 SITE_ID = 1

aiida/backends/tests/common/test_timezone.py

@@ -23,9 +23,14 @@ class TimezoneTest(unittest.TestCase):
     """Tests for the timezone utility module."""
 
     def test_timezone_now(self):
-        """Test timezone.now function."""
+        """Test timezone.now function.
+
+        Check that the time returned by AiiDA's timezone.now() function is compatible
+        with attaching a timezone to a "naive" time stamp using timezone.make_aware().
+        """
         delta = datetime.timedelta(minutes=1)
         ref = timezone.now()
+
         from_tz = timezone.make_aware(datetime.datetime.fromtimestamp(time.time()))
         self.assertLessEqual(from_tz, ref + delta)
         self.assertGreaterEqual(from_tz, ref - delta)

aiida/common/timezone.py

@@ -22,7 +22,14 @@ def get_current_timezone():
     :return: current timezone
     """
     from tzlocal import get_localzone
-    return get_localzone()
+    local = get_localzone()
+
+    if local.zone == 'local':
+        raise ValueError(
+            "Unable to detect name of local time zone. Please set 'TZ' environment variable, e.g."
+            " to 'Europe/Zurich'"
+        )
+    return local
 
 
 def now():
@@ -70,8 +77,10 @@ def make_aware(value, timezone=None, is_dst=None):
 
     if is_aware(value):
         raise ValueError('make_aware expects a naive datetime, got %s' % value)
+
     # This may be wrong around DST changes!
-    return value.replace(tzinfo=timezone)
+    # See http://pytz.sourceforge.net/#localized-times-and-date-arithmetic
+    return timezone.localize(value)
 
 
 def localtime(value, timezone=None):

aiida/manage/backup/backup_base.py

@@ -21,7 +21,6 @@
 from abc import abstractmethod, ABCMeta
 import six
 from dateutil.parser import parse
-from pytz import timezone as ptimezone
 
 from aiida.common import json
 from aiida.common import timezone as dtimezone
@@ -136,11 +135,11 @@ def _read_backup_info_from_dict(self, backup_variables):  # pylint: disable=too-
             try:
                 self._oldest_object_bk = parse(backup_variables.get(self.OLDEST_OBJECT_BK_KEY))
                 if self._oldest_object_bk.tzinfo is None:
-                    curr_timezone = str(dtimezone.get_current_timezone())
-                    self._oldest_object_bk = ptimezone(curr_timezone).localize(self._oldest_object_bk)
+                    curr_timezone = dtimezone.get_current_timezone()
+                    self._oldest_object_bk = dtimezone.get_current_timezone().localize(self._oldest_object_bk)
                     self._logger.info(
                         'No timezone defined in the oldest modification date timestamp. Setting current timezone (%s).',
-                        curr_timezone
+                        curr_timezone.zone
                     )
             # If it is not parsable...
             except ValueError:
@@ -168,13 +167,13 @@ def _read_backup_info_from_dict(self, backup_variables):  # pylint: disable=too-
                 self._end_date_of_backup = parse(backup_variables.get(self.END_DATE_OF_BACKUP_KEY))
 
                 if self._end_date_of_backup.tzinfo is None:
-                    curr_timezone = str(dtimezone.get_current_timezone())
+                    curr_timezone = dtimezone.get_current_timezone()
                     self._end_date_of_backup = \
-                        ptimezone(curr_timezone).localize(
+                        curr_timezone.localize(
                             self._end_date_of_backup)
                     self._logger.info(
                         'No timezone defined in the end date of backup timestamp. Setting current timezone (%s).',
-                        curr_timezone
+                        curr_timezone.zone
                     )
 
                 self._internal_end_date_of_backup = self._end_date_of_backup