vasprun_etree = etree.iterparse(fileptr, tag='varray')

def _get_forces(self, vasprun_etree):
        """
        vasprun_etree = etree.iterparse(fileptr, tag='varray')
        """
        forces = []
        for event, element in vasprun_etree:
            if element.attrib['name'] == 'forces':
                for v in element:
                    forces.append([float(x) for x in v.text.split()])
        return np.array(forces)