TaggedJSONSerializer Class — flask Architecture

Source Code

src/flask/json/tag.py lines 219–327

class TaggedJSONSerializer:
    """Serializer that uses a tag system to compactly represent objects that
    are not JSON types. Passed as the intermediate serializer to
    :class:`itsdangerous.Serializer`.

    The following extra types are supported:

    * :class:`dict`
    * :class:`tuple`
    * :class:`bytes`
    * :class:`~markupsafe.Markup`
    * :class:`~uuid.UUID`
    * :class:`~datetime.datetime`
    """

    __slots__ = ("tags", "order")

    #: Tag classes to bind when creating the serializer. Other tags can be
    #: added later using :meth:`~register`.
    default_tags = [
        TagDict,
        PassDict,
        TagTuple,
        PassList,
        TagBytes,
        TagMarkup,
        TagUUID,
        TagDateTime,
    ]

    def __init__(self) -> None:
        self.tags: dict[str, JSONTag] = {}
        self.order: list[JSONTag] = []

        for cls in self.default_tags:
            self.register(cls)

    def register(
        self,
        tag_class: type[JSONTag],
        force: bool = False,
        index: int | None = None,
    ) -> None:
        """Register a new tag with this serializer.

        :param tag_class: tag class to register. Will be instantiated with this
            serializer instance.
        :param force: overwrite an existing tag. If false (default), a
            :exc:`KeyError` is raised.
        :param index: index to insert the new tag in the tag order. Useful when
            the new tag is a special case of an existing tag. If ``None``
            (default), the tag is appended to the end of the order.

        :raise KeyError: if the tag key is already registered and ``force`` is
            not true.
        """
        tag = tag_class(self)
        key = tag.key

        if key:
            if not force and key in self.tags:
                raise KeyError(f"Tag '{key}' is already registered.")

            self.tags[key] = tag

        if index is None:
            self.order.append(tag)
        else:
            self.order.insert(index, tag)

    def tag(self, value: t.Any) -> t.Any:
        """Convert a value to a tagged representation if necessary."""
        for tag in self.order:
            if tag.check(value):
                return tag.tag(value)

        return value

    def untag(self, value: dict[str, t.Any]) -> t.Any:
        """Convert a tagged representation back to the original type."""
        if len(value) != 1: