input.txt

Cat mouse lion deer Tiger lion Elephant lion deer

mapper.py

#!/usr/bin/python
import sys
#Word Count Example
# input comes from standard input STDIN
for line in sys.stdin:
  line = line.strip() #remove leading and trailing whitespaces
  words = line.split() #split the line into words and returns as a list
  for word in words:
  #write the results to standard output STDOUT
    print('%s\t%s' % (word,1)) #Emit the word

reducer.py

#!/usr/bin/python
import sys
from operator import itemgetter
# using a dictionary to map words to their counts
current_word = None
current_count = 0
word = None
# input comes from STDIN
for line in sys.stdin:
  line = line.strip()
  word,count = line.split('\t',1)
  try:
    count = int(count)
  except ValueError:
    continue
  if current_word == word:
    current_count += count
  else:
    if current_word:
      print('%s\t%s' % (current_word, current_count))
    current_count = count
    current_word = word
if current_word == word:
  print('%s\t%s' % (current_word,current_count))