from mrjob.job import MRJob

class TotalAmountCust(MRJob):

    def mapper(self, _, line):
        (customerid, idno, amount) = line.split(',')
        yield customerid, float(amount)

    def reducer(self, customerid, amount):
        yield customerid, sum(amount)

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

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

class TotalAmountCustSort(MRJob):
    def steps(self):
        return [ MRStep(mapper = self.map_by, reducer = self.red_by),
                MRStep(mapper = self.map_sort, reducer = self.red_sort) ]
    def map_by(self, _, line):
        (customerid, idno, amount) = line.split(',')
        yield customerid.zfill(2), float(amount)
    def red_by(self, customerid, amount):
        yield customerid, '%04.02f' % sum(amount)
    def map_sort(self, customerid, total):
        yield float(total), customerid
    def red_sort(self, total, customerid):
        yield total, customerid
if __name__ == '__main__':
    TotalAmountCustSort.run()