Class Part

src/pptx/opc/package.py:281–379

Base class for package parts. Provides common properties and methods, but intended to be subclassed in client code to implement specific part behaviors. Also serves as the default class for parts that are not yet given specific behaviors.

class Part(_RelatableMixin):
    """Base class for package parts.

    Provides common properties and methods, but intended to be subclassed in client code to
    implement specific part behaviors. Also serves as the default class for parts that are not yet
    given specific behaviors.
    """

    def __init__(
        self, partname: PackURI, content_type: str, package: Package, blob: bytes | None = None
    ):
        # --- XmlPart subtypes, don't store a blob (the original XML) ---
        self._partname = partname
        self._content_type = content_type
        self._package = package
        self._blob = blob

    @classmethod
    def load(cls, partname: PackURI, content_type: str, package: Package, blob: bytes) -> Self:
        """Return `cls` instance loaded from arguments.

        This one is a straight pass-through, but subtypes may do some pre-processing, see XmlPart
        for an example.
        """
        return cls(partname, content_type, package, blob)

    @property
    def blob(self) -> bytes:
        """Contents of this package part as a sequence of bytes.

        Intended to be overridden by subclasses. Default behavior is to return the blob initial
        loaded during `Package.open()` operation.
        """
        return self._blob or b""

    @blob.setter
    def blob(self, blob: bytes):
        """Note that not all subclasses use the part blob as their blob source.

        In particular, the |XmlPart| subclass uses its `self._element` to serialize a blob on
        demand. This works fine for binary parts though.
        """
        self._blob = blob

    @lazyproperty
    def content_type(self) -> str:
        """Content-type (MIME-type) of this part."""
        return self._content_type

    def load_rels_from_xml(self, xml_rels: CT_Relationships, parts: dict[PackURI, Part]) -> None:
        """load _Relationships for this part from `xml_rels`.

        Part references are resolved using the `parts` dict that maps each partname to the loaded
        part with that partname. These relationships are loaded from a serialized package and so
        already have assigned rIds. This method is only used during package loading.
        """
        self._rels.load_from_xml(self._partname.baseURI, xml_rels, parts)