'Adds the subreddit\'s path to the path if another subreddit\'s
prefix is not already present.'

def path_add_subreddit(self, subreddit):

    if (not (self.path_has_subreddit() or self.path.startswith(subreddit.user_path))):
        self.path = (subreddit.user_path + self.path)
    return self
