code: def _flatten(nested_lists):
      return functools.reduce(lambda x, y: x + y, nested_lists, [])
  
imports: import warnings
  import functools
  from collections import namedtuple, Counter, OrderedDict
  import spacy
  import numpy
label_desc: Use image node_id 3 for calling a global function with example usage: _flatten(nested_lists) and returns: functools