<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def post_message(self, channel_id, message, **kwargs):
 """ Send a message using the slack Event API. Event messages should be used for more complex messages. See https://api.slack.com/methods/chat.postMessage for details on arguments can be included with your message. When using the post_message API, to have your message look like it's sent from your bot you'll need to include the `as_user` kwarg. Example of how to do this: server.slack.post_message(msg['channel'], 'My message', as_user=server.slack.username) """

        params = {
            "post_data": {
                "text": message,
                "channel": channel_id,
            }
        }
        params["post_data"].update(kwargs)

        return self.api_call("chat.postMessage", **params)