<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def init_client(client_id):
 """Initialse a driver for client and store for future reference @param client_id: ID of client user @return whebwhatsapi object """

    if client_id not in drivers:
        drivers[client_id] = init_driver(client_id)
    return drivers[client_id]