pymysql.err.OperationalError: (2003, "Can't connect to MySQL server on 'localhost'

[JACKGELOVE]

运行python chatdb.py后报错

ConnectionRefusedError: [Errno 111] Connection refused

During handling of the above exception, another exception occurred:
pymysql.err.OperationalError: (2003, "Can't connect to MySQL server on 'localhost' ([Errno 111] Connection refused)")

File "/home/Documents/git_clone/ChatDB/mysql.py", line 59, in execute_sql
self.conn.rollback()
AttributeError: 'NoneType' object has no attribute 'rollback'