[
   {
    "url":Stackoverflow.com/login,
    "count": 200.654,
    "browsers":[
      Firefox 33,
      IE 7,
      Opera
    ]
   },
   {..},
   {..}
 ],

FULL_URL_WHERE_DOMAIN_EQUALS = mySuperCoolRegex

class MRReferralAnalysis(MRJob):

    def mapper(self, _, line):

        for group in FULL_URL_WHERE_DOMAIN_EQUALS.findall(line):
            yield (group, 1)

    def reducer(self, itemOfInterest, counts):
        yield (sum(counts), itemOfInterest)

    def steps(self):
        return [
            MRStep( mapper=self.mapper,
                    reducer=self.reducer)
        ]

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