A map-reduce class in Python, with the typical "hello, world!" word-counting example. You can download ulysses.txt file used in the example here: http://www.gutenberg.org/ebooks/4300

mapreduce.py

from collections import defaultdict
import abc

class MapReducer(object):

    __metaclass__ = abc.ABCMeta

    @abc.abstractmethod
    def map(self,items):
        return []

    @abc.abstractmethod
    def reduce(self,key,values):
        return []

    def filter(self,items):
        return items

    def mapreduce(self,items):
        map_results = [item for sublist in [self.map(item) for item in self.filter(items)] for item in sublist if item]
        grouped_results = defaultdict(lambda :[])
        for key,value in map_results:
            grouped_results[key].append(value)
        return dict([(key,self.reduce(key,values)) for key,values in grouped_results.items()])

z_example.py

import pprint
from mapreduce import MapReducer
from collections import defaultdict

class WordReducer(MapReducer):

  def map(self,item):
    frequencies = defaultdict(lambda :0)
    for word in item.strip().split():
      frequencies[word.lower()]+=1
    return frequencies.items()

  def reduce(self,key,values):
    return sum(values)

if __name__ == '__main__':
  with open('ulysses.txt','r') as f:
    lines = f.read().split("\n")
  map_reducer = WordReducer()
  result = map_reducer.mapreduce(lines)
  pprint.pprint(sorted(result.items(),key = lambda x:-x[1])[:100])

zz_output

[('the', 14850),
 ('of', 8212),
 ('and', 7051),
 ('a', 6403),
 ('to', 4912),
 ('in', 4796),
 ('he', 3620),
 ('his', 3275),
 ('with', 2485),
 ('i', 2442),
 ('that', 2336),
 ('was', 2037),
 ('on', 1979),
 ('for', 1901),
 ('it', 1874),
 ('you', 1604),
 ('her', 1585),
 ('is', 1301),
 ('at', 1279),
 ('by', 1247),
 ('all', 1207),
 ('as', 1166),
 ('him', 1123),
 ('from', 1075),
 ('she', 1021),
 ('or', 1004),
 ('they', 981),
 ('be', 846),
 ('not', 840),
 ('my', 815),
 ('had', 790),
 ('out', 782),
 ('what', 762),
 ('their', 710),
 ('like', 706),
 ('mr', 701),
 ('up', 674),
 ('have', 658),
 ('an', 652),
 ('me', 647),
 ('but', 644),
 ('one', 573),
 ('if', 539),
 ('so', 538),
 ('when', 531),
 ('there', 508),
 ('about', 504),
 ('them', 498),
 ('are', 498),
 ('were', 489),
 ('your', 486),
 ('said.', 480),
 ('then', 477),
 ('which', 474),
 ('old', 469),
 ('no', 462),
 ('says', 454),
 ('bloom', 442),
 ('this', 439),
 ('said', 428),
 ('who', 423),
 ('over', 401),
 ('we', 393),
 ('after', 388),
 ('down', 380),
 ('would', 369),
 ('do', 364),
 ('did', 358),
 ('two', 345),
 ('into', 328),
 ('see', 317),
 ('stephen', 316),
 ('will', 316),
 ('those', 311),
 ('off', 309),
 ('its', 305),
 ('some', 305),
 ('could', 297),
 ('our', 284),
 ('bloom:', 284),
 ('man', 283),
 ('little', 283),
 ('has', 282),
 ('other', 282),
 ('good', 276),
 ('where', 275),
 ('too', 274),
 ('said,', 265),
 ('more', 261),
 ('back', 256),
 ('time', 254),
 ('now', 252),
 ('get', 251),
 ('only', 243),
 ('know', 243),
 ('through', 242),
 ('how', 242),
 ('it.', 239),
 ('just', 238),
 ('never', 236)]