code: def args_priority(args, environ):
      '''
          priority of token
          1) as argumment: -t
          2) as environ variable
  
          priority of as_user
          1) as argument: -a
          2) as environ variable
      '''
  
      arg_token = args.token
      arg_as_user = args.as_user
  
      slack_token_var_name = 'SLACK_TOKEN'
      if slack_token_var_name in environ.keys():
          token = environ[slack_token_var_name]
      else:
          token = None
  
      if arg_token:
          token = arg_token
  
      # slack as_user
      slack_as_user_var_name = 'SLACK_AS_USER'
      as_user = bool(environ.get(slack_as_user_var_name))
  
      if arg_as_user:
          as_user = True
  
      return token, as_user, args.channef args_priority(args, environ):
      '''
          priority of token
          1) as argumment: -t
          2) as environ variable
  
          priority of as_user
          1) as argument: -a
          2) as environ variable
      '''
  
      arg_token = args.token
      arg_as_user = args.as_user
  
      slack_token_var_name = 'SLACK_TOKEN'
      if slack_token_var_name in environ.keys():
          token = environ[slack_token_var_name]
      else:
          token = None
  
      if arg_token:
          token = arg_token
  
      # slack as_user
      slack_as_user_var_name = 'SLACK_AS_USER'
      as_user = bool(environ.get(slack_as_user_var_name))
  
      if arg_as_user:
          as_user = True
  
      return token, as_user, args.channel
docs: priority of token
          1) as argumment: -t
          2) as environ variable
  
          priority of as_user
          1) as argument: -a
          2) as environ variable