错误信息：You're using the Django "sites framework" without having set the SITE_ID setting. Create a site in your database and set the SITE_ID setting to fix this error.
  原因：settings.py里# Application definition中添加了'django.contrib.sites'模块后需要设置SITE_ID 
  处理：在settings.py里添加配置：SITE_ID = 1

Database returned an invalid value in QuerySet.datetimes(). Are time zone definitions for your database and pytz installed?

mysql_tzinfo_to_sql /usr/share/zoneinfo | mysql -u root -p mysql