Request the user stats for a given game.

        steamID: The users ID
        appID: The app id
        format: Return format. None defaults to json. (json, xml, vdf)

def get_user_stats_for_game(self, steamID, appID, format=None):
        """Request the user stats for a given game.

        steamID: The users ID
        appID: The app id
        format: Return format. None defaults to json. (json, xml, vdf)

        """
        parameters = {'steamid' : steamID, 'appid' : appID}
        if format is not None:
            parameters['format'] = format
        url = self.create_request_url(self.interface, 'GetUserStatsForGame', 2,
            parameters)
        data = self.retrieve_request(url)
        return self.return_data(data, format=format)