code: def _defined_keys(dict_):
      return {k for k, v in dict_.items() if v is not None}
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import collections
  from graph_nets import graphs
  import networkx
  import numpy
  from six.moves import range
  from six.moves import zip
label_desc: Use image node_id 2 for calling a global function with example usage: _defined_keys(dict_) and returns: unknown