虽然PyPI软件包称为 slackclient ，但是您使用名称slack导入模块:

While the PyPI package is called slackclient, you import the module using the name slack:

import slack

或者，例如:

from slack import WebClient

参考: https://github.com/slackapi/python-slackclient/wiki/Migrating-to-2.x