@lazyproperty
    def numbering_part(self):
        try:
            return self.part_related_by(RT.NUMBERING)
        except KeyError:
            numbering_part = NumberingPart.new()
            self.relate_to(numbering_part, RT.NUMBERING)
            return numbering_part
A |NumberingPart| object providing access to the numbering
dataset/ETHPy150Open python-openxml/python-docx/docx/parts/document.py/DocumentPart.numbering_part