Class _RelatableMixin

src/pptx/opc/package.py:30–66

Provide relationship methods required by both the package and each part.

class _RelatableMixin:
    """Provide relationship methods required by both the package and each part."""

    def part_related_by(self, reltype: str) -> Part:
        """Return (single) part having relationship to this package of `reltype`.

        Raises |KeyError| if no such relationship is found and |ValueError| if more than one such
        relationship is found.
        """
        return self._rels.part_with_reltype(reltype)

    def relate_to(self, target: Part | str, reltype: str, is_external: bool = False) -> str:
        """Return rId key of relationship of `reltype` to `target`.

        If such a relationship already exists, its rId is returned. Otherwise the relationship is
        added and its new rId returned.
        """
        if isinstance(target, str):
            assert is_external
            return self._rels.get_or_add_ext_rel(reltype, target)

        return self._rels.get_or_add(reltype, target)

    def related_part(self, rId: str) -> Part:
        """Return related |Part| subtype identified by `rId`."""
        return self._rels[rId].target_part

    def target_ref(self, rId: str) -> str:
        """Return URL contained in target ref of relationship identified by `rId`."""
        return self._rels[rId].target_ref

    @lazyproperty
    def _rels(self) -> _Relationships:
        """|_Relationships| object containing relationships from this part to others."""
        raise NotImplementedError(  # pragma: no cover
            "`%s` must implement `.rels`" % type(self).__name__
        )


class OpcPackage(_RelatableMixin):