MR job to calculate movie's popularity

PopularityBreakdown.py

from mrjob.job import MRJob
from mrjob.step import MRStep

class PopularityBreakdown(MRJob):
    def steps(self):
        return [
            MRStep(mapper=self.mapper_ratings,
                   reducer=self.reducer_ratings),
            MRStep(reducer=self.reducer_sortings)
        ]
    def mapper_ratings(self, _, line):
        (userID, movieID, rating, timestamp) = line.split('\t')
        yield movieID, 1

    def reducer_ratings(self, key, values):
        yield str(sum(values)).zfill(5), key

    def reducer_sortings(self,count,movies):
        for movie in movies:
            yield movie,count


if __name__ == '__main__':
    PopularityBreakdown.run()