how to upload a file with SlackClient library

slack_uploader.py

from slackclient import SlackClient

class SlackBot(object):
    '''
    SlackBot:
    '''
    
    def __init__(self, logger, slackclient):
        self.logger = logger or logging.getLogger(__name__)
        self.slack_client = slackclient or SlackClient(os.environ.get('SLACK_BOT_TOKEN'))
    
    def send_message(self, msg, attachment=None, channel="#general"):
        '''
        Plain send text method
        '''
        try:
            res = self.slack_client.api_call("chat.postMessage", channel=channel, text=msg, attachments=attachment, as_user=True)
            if not res.get('ok'):
                self.logger.error('error: {}', res.get('error'))
        except:
            self.logger.exception('send_message failed')
    
    def upload_file(self, filename, content, channel):
        '''
        upload a long text as a file
        '''
        ret = self.slack_client.api_call("files.upload", filename=filename, channels=channel, file= io.BytesIO(str.encode(content)))
        if not 'ok' in ret or not ret['ok']:
            # error
            self.logger.error('fileUpload failed %s', ret['error'])