mapper.py

#!/usr/bin/env python
\"\"\"A more advanced Mapper, using Python iterators and generators.\"\"\"

import sys

def read_input(file):
    for line in file:
        # split the line into words
        yield line.split()

def main(separator=\'\\t\'):
    # input comes from STDIN (standard input)
    data = read_input(sys.stdin)
    for words in data:
        # write the results to STDOUT (standard output);
        # what we output here will be the input for the
        # Reduce step, i.e. the input for reducer.py
        #
        # tab-delimited; the trivial word count is 1
        for word in words:
            print \'%s%s%d\' % (word, separator, 1)

if __name__ == \"__main__\":
    main()

reducer.py

#!/usr/bin/env python
\"\"\"A more advanced Reducer, using Python iterators and generators.\"\"\"

from itertools import groupby
from operator import itemgetter
import sys

def read_mapper_output(file, separator=\'\\t\'):
    for line in file:
        yield line.rstrip().split(separator, 1)

def main(separator=\'\\t\'):
    # input comes from STDIN (standard input)
    data = read_mapper_output(sys.stdin, separator=separator)
    # groupby groups multiple word-count pairs by word,
    # and creates an iterator that returns consecutive keys and their group:
    #   current_word - string containing a word (the key)
    #   group - iterator yielding all [\"<current_word>\", \"<count>\"] items
    for current_word, group in groupby(data, itemgetter(0)):
        try:
            total_count = sum(int(count) for current_word, count in group)
            print \"%s%s%d\" % (current_word, separator, total_count)
        except ValueError:
            # count was not a number, so silently discard this item
            pass

if __name__ == \"__main__\":
    main()

转自：http://www.michael-noll.com/tutorials/writing-an-hadoop-mapreduce-program-in-python/