from mrjob.job import MRJob

class MRRatingCounter(MRJob):
    def mapper(self, key, line):
        (userID, movieID, rating, timestamp) = line.split("t")
        yield rating, 1

    def reducer(self, rating, occurences):
        yield rating, sum(occurences)

if __name__ == "main__":
    MRRatingCounter.run()

filepath = "01.ml-100k/u.data"

MRRatingCounter(filepath)