.. _py-dg/VertexMapper:

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dg/VertexMapper
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.. default-domain:: py

.. py:currentmodule:: mod
.. cpp:namespace:: mod

.. class:: DGVertexMapper

    A class for enumerating all valid vertex maps for a given :class:`DGHyperEdge`.
    That is, for such a hyperedge, collect the graphs associated with
    respectively the source and target vertices, and create the disjoint union of those graphs.
    Let the result be the graphs :math:`G` and :math:`H`.
    Then each rule :math:`r` associated with the hyperedge,
    calculate each direct derivation :math:`G \overset{r}{\Rightarrow} H` and record the associated
    vertex maps :math:`V(G) \rightarrow V(H)`.
    Those maps are available in this class.

    .. method:: __init__(e)

        Perform the vertex map calculation.

        :param DGHyperEdge e: the hyperedge to calculate vertex maps for.
        :raises: :class:`LogicError` if ``not e``.
    .. attribute:: edge

        (Read-only) The hyperedge to calculate vertex maps for.

        :type: DGHyperEdge
    .. attribute:: left
                   right

        :returns: the disjoint union of graphs from respectively the source and target vertices of the hyperedge.
            That is, the graphs :math:`G` and :math:`H` that are the domain and codomain graphs of the calculated
            vertex maps.
        :type: UnionGraph
    .. method:: __iter__()

        :returns: an iterator over the vertex maps,
            see :meth:`__getitem__` for the specific type.
    .. attribute:: size

        (Read-only) The number of vertex maps calculated.

        :type: int
    .. method:: __len__()

        :returns: :attr:`size`
        :rtype: int
    .. method:: __getitem__(i)

        :param int i: the index of the map to retrieve.
        :returns: the ``i``\ th vertex map.
        :rtype: tuple[Rule, VertexMapUnionGraphUnionGraph]
        :raises: :class:`LogicError` if ``i`` is out of range.