httk.atomistic.models.sites.api
===============================

.. py:module:: httk.atomistic.models.sites.api

.. autoapi-nested-parse::

   The minimal canonical sites interface for httk-atomistic.



Classes
-------

.. autoapisummary::

   httk.atomistic.models.sites.api.SitesAPI


Module Contents
---------------

.. py:class:: SitesAPI

   Bases: :py:obj:`abc.ABC`


   Abstract base class for the canonical sites interface.

   It declares the single ``reduced_coords`` accessor (the exact Nx3 rational
   :class:`~httk.core.FracVector` of reduced coordinates) that every sites backend produces from
   its own native representation and every sites view builds its presentation from. This is the
   single interchange format; there is no pairwise conversion between backends.


   .. py:property:: reduced_coords
      :type: httk.core.FracVector

      :abstractmethod:


      Return the reduced site coordinates.


   .. py:property:: num_sites
      :type: int


      Return the number of coordinate rows.

      :return: The number of sites.


   .. py:property:: precision
      :type: fractions.Fraction | None


      How precisely the coordinates were stated, in fractional units, or ``None``.

      Fractional, not a length: reduced coordinates are dimensionless and a ``Sites`` has
      no cell to convert with. :meth:`~httk.atomistic.UnitcellStructure.cartesian_precision`
      does the conversion, where the cell is known.

      Concrete rather than abstract, so a backend with no source of precision inherits
      ``None`` instead of breaking.

      :return: The fractional precision, or ``None`` when unknown.