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qml.data.field

field(attribute_type=UnsetType.UNSET, doc=None, py_type=None, **kwargs)[source]

Used to define fields on a declarative Dataset.

Parameters:

  • attribute_type – DatasetAttribute class for this attribute. If not provided, type may be derived from the type annotation on the class.

  • doc – Documentation for the attribute

  • py_type – Type annotation or string describing this object’s type. If not provided, the annotation on the class will be used

  • kwargs – Extra arguments to AttributeInfo

Return type:

Field

See also

Dataset, attribute()

Example

The datasets declarative API allows us to create subclasses of Dataset that define the required attributes, or ‘fields’, and their associated type and documentation:

class QuantumOscillator(qml.data.Dataset, data_name="quantum_oscillator", identifiers=["mass", "force_constant"]):
    """Dataset describing a quantum oscillator."""

    mass: float = qml.data.field(doc = "The mass of the particle")
    force_constant: float = qml.data.field(doc = "The force constant of the oscillator")
    hamiltonian: qml.Hamiltonian = qml.data.field(doc = "The hamiltonian of the particle")
    energy_levels: np.ndarray = qml.data.field(doc = "The first 1000 energy levels of the system")

The data_name keyword argument specifies a category or descriptive name for the dataset type, and the identifiers keyword argument specifies fields that function as parameters, i.e., they determine the behaviour of the system.

When a QuantumOscillator dataset is created, its attributes will have the documentation from the field definition:

>>> dataset = QuantumOscillator(
...     mass=1,
...     force_constant=0.5,
...     hamiltonian=qml.X(0),
...     energy_levels=np.array([0.1, 0.2])
... )
>>> dataset.attr_info["mass"]["doc"]
'The mass of the particle'
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