Why can reading obj ['segmentation '] generate rle and rles? Rles is iterative, and rle is not iterative.

[liudadan]

Why can reading obj ['segmentation '] generate rle and rles? Rles is iterative, and rle is not iterative.
def get_mask(self, anno, img_info):
m = np.zeros((img_info['height'], img_info['width']))

    for obj in anno:
        if obj['iscrowd']:
            rle = pycocotools.mask.frPyObjects(
                obj['segmentation'], img_info['height'], img_info['width'])
            m += pycocotools.mask.decode(rle)
        elif obj['num_keypoints'] == 0:
            rles = pycocotools.mask.frPyObjects(
                obj['segmentation'], img_info['height'], img_info['width'])
            for rle in rles:
                m += pycocotools.mask.decode(rle)

    return m < 0.5