def __init__(self, circuit, direct=False, executable=None):
## If circuit is a string, assume it's a netlist and create a circuit
if type(circuit) == types.StringType:
circuit = Circuit(circuit)
super(Simulation, self).__init__(circuit)
if direct:
self.session = GnucapSessionDirect()
else:
self.session = GnucapSessionPexpect(executable)
if circuit is not None and not isinstance(circuit, Circuit):
raise ValueError('Circuit instance must be a %s instance' %
str(Circuit))
if circuit is not None:
self.update_netlist()