old_contents: # -*- coding: utf-8 -*-
  
  from __future__ import unicode_literals
  
  """
  Convert a flat list representing pairs of words into a list of lists.
    ex. [a, b, c, d] -> [[a,b], [c,d]]
  Returned as a generator.
  """
  def pairs(arr):
      size = 2
      for i in range(0, len(arr)-1, size):
          yield arr[i:i+size]
  
  
new_contents: # -*- coding: utf-8 -*-
  
  from __future__ import unicode_literals
  
subject: Remove unneeded flattening code.