<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get(self, key, get_cas=False):
 """ Get a key from server. :param key: Key's name :type key: six.string_types :param get_cas: If true, return (value, cas), where cas is the new CAS value. :type get_cas: boolean :return: Returns a key data from server. :rtype: object """

        for server in self.servers:
            value, cas = server.get(key)
            if value is not None:
                if get_cas:
                    return value, cas
                else:
                    return value
        if get_cas:
            return None, None