# Observable¶

Module: pennylane

class Observable(*args, wires=None, do_queue=True)[source]

Base class for observables supported by a device.

Observable is used to describe Hermitian quantum observables.

As with Operation, the following class attributes must be defined for all observables:

The following two class attributes are optional, but in most cases should be clearly defined to avoid unexpected behavior during differentiation.

Parameters: Keyword Arguments: args (tuple[float, int, array, Variable]) – observable parameters wires (Sequence[int]) – subsystems it acts on. Currently, only one subsystem is supported. do_queue (bool) – Indicates whether the operation should be immediately pushed into a QNode observable queue. This flag is useful if there is some reason to call an observable outside of a QNode context.