Python TypeError: coercing to Unicode: need string or buffer, float found

调试Python程序：

unique_key = name + time.mktime(create_time.timetuple())

提示错误：

TypeError: coercing to Unicode: need string or buffer, float found

错误原因：使用“+”拼接会抛出异常，改用%操作符输出

    unique_key = u'%s%s' % (name, time.mktime(create_time.timetuple()))