An object representing a single input port.
How the port is identified internally is backend-dependent.
If the backend allows it, port objects remain valid when
other ports in the system change (i.e. it is not just an index).
An object representing a single output port.
How the port is identified internally is backend-dependent.
If the backend allows it, port objects remain valid when
other ports in the system change (i.e. it is not just an index).