True if this shape is an auto shape. A shape is an auto shape if it
        has a ``<a:prstGeom>`` element and does not have a txBox="1" attribute
        on cNvSpPr.

def is_autoshape(self):
        """
        True if this shape is an auto shape. A shape is an auto shape if it
        has a ``<a:prstGeom>`` element and does not have a txBox="1" attribute
        on cNvSpPr.
        """
        prstGeom = self.prstGeom
        if prstGeom is None:
            return False
        if self.nvSpPr.cNvSpPr.txBox is True:
            return False
        return True