def ban(roomJID, entity, reason=None, sender=None):
    """
        Ban a user from a MUC room.

        @param roomJID: The bare JID of the room.
        @type roomJID: L{JID<twisted.words.protocols.jabber.jid.JID>}

        @param entity: The bare JID of the entity to be banned.
        @type entity: L{JID<twisted.words.protocols.jabber.jid.JID>}

        @param reason: The reason for banning the entity.
        @type reason: C{unicode}

        @param sender: The entity sending the request.
        @type sender: L{JID<twisted.words.protocols.jabber.jid.JID>}
        """
