解决 pymysql : AttributeError: 'NoneType' object has no attribute 'encode'

pymysql连结mysql数据库时报错：
AttributeError: 'NoneType' object has no attribute 'encode'
错误原因:

1. pymysql.connect()中charset为’utf8’而不是’utf-8’
2. 配置文件key值加了单引号

pymysql连结数据库：

import pymysql
try:
	self.conn = pymysql.connect(host=host,port=port,user=username,passwd=passwd,db=database,charset=charasest)
except Exception as e:
	print (e)
else:
     print ('connect success {0}'.format(host))
     self.cur = self.conn.cursor()