def blueprint(self) -> str | None:
        """The registered name of the current blueprint.

        This will be ``None`` if the endpoint is not part of a
        blueprint, or if URL matching failed or has not been performed
        yet.

        This does not necessarily match the name the blueprint was
        created with. It may have been nested, or registered with a
        different name.
        """
        endpoint = self.endpoint

        if endpoint is not None and "." in endpoint:
            return endpoint.rpartition(".")[0]

        return None
The registered name of the current blueprint.

        This will be ``None`` if the endpoint is not part of a
        blueprint, or if URL matching failed or has not been performed
        yet.

        This does not necessarily match the name the blueprint was
        created with. It may have been nested, or registered with a
        different name.
        
src/flask/wrappers.py