added new folders

back_end/cron_job.py

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+# delete from cache
+# where created_at < now() - interval '3 days';
+import os
+import datetime
+import sqlalchemy
+from sqlalchemy.schema import Table
+from sqlalchemy.schema import MetaData
+
+print 'Running cron job'
+
+
+too_old = datetime.datetime.today() - datetime.timedelta(days=3)
+db_url = os.environ.get('DATABASE_URL', 'postgresql:///wesworld')
+engine = sqlalchemy.create_engine(db_url)
+meta = MetaData()
+meta.reflect(bind=engine)
+cache_table = meta.tables['cache']
+engine.execute(cache_table.delete().where(cache_table.c.created_at <= too_old))