new_contents: #!/usr/bin/env python
  
  from operator import itemgetter
  import sys
  
  current_word = None
  current_count = 0
  word = None
  
  
  for line in sys.stdin:    # input comes from STDIN
      line = line.strip()    # remove leading and trailing whitespace
  
      word, count = line.split('\t', 1)    # parse the input we got from mapper.py
  
      try:    # convert count (currently a string) to int
          count = int(count)
      except ValueError:
          # count was not a number, so silently
          # ignore/discard this line
          continue
  
      # this IF-switch only works because Hadoop sorts map output
      # by key (here: word) before it is passed to the reducer
      if current_word == word:
          current_count += count
      else:
          if current_word:
              # write result to STDOUT
              print '%s\t%s' % (current_word, current_count)
          current_count = count
          current_word = word
  
  # do not forget to output the last word if needed!
  if current_word == word:
      print '%s\t%s' % (current_word, current_count)
  
subject: Create wordcount-reducer.py