old_contents: from django.conf import settings
  from django.utils import timezone
  
  try:
      import pytz
  except ImportError:
      pytz = None
  
  def timezones(request):
      alt_timezone = request.session.get('alt_timezone', pytz.utc)
      return {
          'pytz': pytz,
          'default_timezone_name': settings.TIME_ZONE,
          'timezones': pytz.common_timezones if pytz else [],
          'alt_timezone': alt_timezone if pytz else timezone.utc,
          'alt_timezone_name': alt_timezone.zone if pytz else 'UTC',
      }
  
new_contents: from django.conf import settings
  from django.utils import timezone
  
  try:
      import pytz
  except ImportError:
      pytz = None
  
  def timezones(request):
      alt_timezone = request.session.get('alt_timezone', (pytz or timezone).utc)
      return {
          'pytz': pytz,
          'default_timezone_name': settings.TIME_ZONE,
          'timezones': pytz.common_timezones if pytz else [],
          'alt_timezone': alt_timezone if pytz else timezone.utc,
          'alt_timezone_name': alt_timezone.zone if pytz else 'UTC',
      }
  
subject: Fix a bug when pytz isn't installed.