docs: def instances(self, **kwargs):
          """
          Retrieve the instances of this `Part` as a `PartSet`.
  
          For instance, if you have a model part, you can get the list of instances that are created based on this
          moodel. If there are no instances (only possible if the multiplicity is :attr:`enums.Multiplicity.ZERO_MANY`)
          than a :exc:`NotFoundError` is returned
  
          .. versionadded:: 1.8
  
          :return: the instances of this part model :class:`PartSet` with category `INSTANCE`
          :raises NotFoundError: if no instances found
  
          Example
          -------
          >>> wheel_model = project.model('Wheel')
          >>> wheel_instance_set = wheel_model.instances()
  
          An example with retrieving the front wheels only using the 'name__contains' search argument.
  
          >>> wheel_model = project.model('Wheel')
          >>> front_wheel_instances = wheel_model.instances(name__contains='Front')
  
          """
          if self.category == Category.MODEL:
              return self._client.parts(model=self, category=Category.INSTANCE, **kwargs)
          else:
              raise NotFoundError("Part {} is not a model".format(self.name))