def get_app_key(self):
        """
        If app_key is not provided will look in environment
        variables for username.
        """
        if self.app_key is None:
            if os.environ.get(self.username):
                self.app_key = os.environ.get(self.username)
            else:
                raise AppKeyError(self.username)
If app_key is not provided will look in environment
        variables for username.