Return new |MediaPart| instance containing *media*.

        *media* must be a |Media| object.

def new(cls, package, media):
        """Return new |MediaPart| instance containing *media*.

        *media* must be a |Media| object.
        """
        partname = package.next_media_partname(media.ext)
        return cls(partname, media.content_type, media.blob, package)