text: import doctest
  from collections import Counter
  
  def sum_counters(counters):
      """Aggregate collections.Counter objects by summing counts
  
      :param counters: list/tuple of counters to sum
      :return: aggregated counters with counts summed
  
      >>> d1 = text_analyzer.Document('1 2 fizz 4 buzz fizz 7 8')
      >>> d2 = text_analyzer.Document('fizz buzz 11 fizz 13 14')
      >>> sum_counters([d1.word_counts, d2.word_counts])
      Counter({'buzz': 2, 'fizz': 4})
      """
      return sum(counters, Counter())
  
  doctest.testmod()
  
  
  '''
  <script.py> output:
      **********************************************************************
      File "__main__", line 9, in NoName
      Failed example:
          sum_counters([d1.word_counts, d2.word_counts])
      Expected:
          Counter({'buzz': 2, 'fizz': 4})
      Got:
          Counter({'fizz': 4, 'buzz': 2})
  '''