# Attribute

class `openff.evaluator.attributes.``Attribute`(docstring, type_hint, default_value=<openff.evaluator.attributes.attributes.UndefinedAttribute object>, optional=False, read_only=False)

  A custom descriptor used to add useful metadata to class attributes.

  This decorator expects the object to have a matching private field in addition to the public attribute. For example if an object has an attribute substance, the object must also have a _substance field.

  Notes

  The attribute class will automatically create this private attribute on the object and populate it with the default value.

  `__init__`(docstring, type_hint, default_value=<openff.evaluator.attributes.attributes.UndefinedAttribute object>, optional=False, read_only=False)

    Initializes a new Attribute object.

    Parameters

      - docstring (str) – A docstring describing the attributes purpose. This will automatically be decorated with additional information such as type hints, default values, etc.

      - type_hint (type , typing.Union) – The expected type of this attribute. This will be used to help the workflow engine ensure that expected input types match corresponding output values.

      - default_value (Any) – The default value for this attribute.

      - optional (bool) – Defines whether this is an optional input of a class. If true, the default_value should be set to UNDEFINED.

      - read_only (bool) – Defines whether this attribute is read-only.

  Methods

  `__init__`(docstring, type_hint[, …]) | Initializes a new Attribute object.