Class _Relationships

src/pptx/opc/package.py:493–677

Collection of |_Relationship| instances having `dict` semantics. Relationships are keyed by their rId, but may also be found in other ways, such as by their relationship type. |Relationship| objects are keyed by their rId. Iterating this collection has normal mapping semantics, generat

class _Relationships(Mapping[str, "_Relationship"]):
    """Collection of |_Relationship| instances having `dict` semantics.

    Relationships are keyed by their rId, but may also be found in other ways, such as by their
    relationship type. |Relationship| objects are keyed by their rId.

    Iterating this collection has normal mapping semantics, generating the keys (rIds) of the
    mapping. `rels.keys()`, `rels.values()`, and `rels.items() can be used as they would be for a
    `dict`.
    """

    def __init__(self, base_uri: str):
        self._base_uri = base_uri

    def __contains__(self, rId: object) -> bool:
        """Implement 'in' operation, like `"rId7" in relationships`."""
        return rId in self._rels

    def __getitem__(self, rId: str) -> _Relationship:
        """Implement relationship lookup by rId using indexed access, like rels[rId]."""
        try:
            return self._rels[rId]
        except KeyError:
            raise KeyError("no relationship with key '%s'" % rId)

    def __iter__(self) -> Iterator[str]:
        """Implement iteration of rIds (iterating a mapping produces its keys)."""
        return iter(self._rels)

    def __len__(self) -> int:
        """Return count of relationships in collection."""
        return len(self._rels)

    def get_or_add(self, reltype: str, target_part: Part) -> str:
        """Return str rId of `reltype` to `target_part`.

        The rId of an existing matching relationship is used if present. Otherwise, a new
        relationship is added and that rId is returned.
        """
        existing_rId = self._get_matching(reltype, target_part)
        return (
            self._add_relationship(reltype, target_part) if existing_rId is None else existing_rId
        )

    def get_or_add_ext_rel(self, reltype: str, target_ref: str) -> str:
        """Return str rId of external relationship of `reltype` to `target_ref`.

        The rId of an existing matching relationship is used if present. Otherwise, a new
        relationship is added and that rId is returned.
        """
        existing_rId = self._get_matching(reltype, target_ref, is_external=True)
        return (
            self._add_relationship(reltype, target_ref, is_external=True)
            if existing_rId is None
            else existing_rId
        )

    def load_from_xml(