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Abstract Instruments and parameters¶

Abstract parameters allow us to create abstract instrument types which are guaranteed to have certain parameters present. For instance, this will allow us to create a unified interface for all voltage sources.

Note: An instrument which contains abstract parameters shall be called an ‘Abstract Instrument’

[1]:

fromqcodes.instrumentimport Instrument

[2]:

classBaseVoltageSource(Instrument):
"""
 All abstract parameters *must* be implemented
 before this class can be initialized. This
 allows us to enforce an interface.
 """
 def__init__(self, name: str):
 super().__init__(name)
 self.voltage = self.add_parameter("voltage", unit="V", abstract=True)
 self.current = self.add_parameter(
 "current", unit="A", get_cmd=None, set_cmd=None
 )

We cannot instantiate a Instrument with abstract parameters.¶

[3]:

try:
 bv = BaseVoltageSource("name")
except NotImplementedError as error:
 print(f"Error: {error}")

Error: <BaseVoltageSource: name> has un-implemented Abstract Parameter and cannot be initialized

Instruments which fail to initialize are not registered:

[4]:

BaseVoltageSource.instances()

[4]:

[]

Units of parameters defined in sub classes must match units defined in the base class¶

[5]:

classWrongSource2(BaseVoltageSource):
"""
 We implement the voltage paramter with the wrong unit
 """
 def__init__(self, name: str, *args, **kwargs):
 super().__init__(name, *args, **kwargs)
 self.add_parameter("voltage", unit="mV")

[6]:

try:
 WrongSource2("name4")
except ValueError as error:
 print(f"Error: {error}")

Error: The unit of the parameter 'voltage' is 'mV'. This is inconsistent with the unit defined in the base class

Instruments which fail to initialize due to the wrong unit are also not registered:

[7]:

BaseVoltageSource.instances()

[7]:

[]

Working subclass¶

[8]:

classVoltageSource(BaseVoltageSource):
"""
 We implement the voltage paramter with the correct unit.
 Here we just implement it as a manual parameter but in a
 real instrument we would probably not do that.
 """
 def__init__(self, name: str, *args, **kwargs):
 super().__init__(name, *args, **kwargs)
 self.voltage = self.add_parameter(
 "voltage", unit="V", set_cmd=None, get_cmd=None
 )

[9]:

vs = VoltageSource("name")

[10]:

vs.voltage(1)

[11]:

vs.voltage()

[11]:

1

This instrument is registered as expected.

[12]:

VoltageSource.instances()

[12]:

[<VoltageSource: name>]