def interval_overlap(interval_1, interval_2):
    x1, x2 = interval_1
    x3, x4 = interval_2
    if x3 < x1:
        return 0 if x4 < x1 else (min(x2,x4) - x1)
    else:
        return 0 if x2 < x3 else (min(x2,x4) - x3)

def bbox_iou(box1, box2):
    # Intersection over Union
    intersect_w = interval_overlap([box1.xmin, box1.xmax], [box2.xmin, box2.xmax])
    intersect_h = interval_overlap([box1.ymin, box1.ymax], [box2.ymin, box2.ymax])
    intersect_area = intersect_w * intersect_h
    
    w1, h1 = box1.xmax-box1.xmin, box1.ymax-box1.ymin
    w2, h2 = box2.xmax-box2.xmin, box2.ymax-box2.ymin
    
    union_area = w1*h1 + w2*h2 - intersect_area
    return float(intersect_area) / union_area