code: def _box_union(a, b):
      i = _box_intersection(a, b)
      u = a.w * a.h + b.w * b.h - i
      return u
  
imports: from __future__ import division
  import math
  from collections import namedtuple
  from functools import cmp_to_key
  import numpy
label_desc: Use image node_id 5 for calling a global function with example usage: _box_union(a, b) and returns: u