code: def calc_begin_idx(idx, step_size, idx_diff):
      return np.max([0, idx - step_size + 1, 2 - idx_diff])
  
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 16 for calling a global function with example usage: calc_begin_idx(idx, step_size, idx_diff) and returns: np