code: def calc_exclusion_start(idx, exclusion_zone):
      return int(np.max([0, idx - exclusion_zone]))
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from __future__ import unicode_literals
  import math
  import time
  import warnings
  import numpy
label_desc: Use image node_id 7 for calling a global function with example usage: calc_exclusion_start(idx, exclusion_zone) and returns: int