Sum the events for each day using the reduce algorithm.

Log analysis

# Sum the events for each day using the reduce algorithm.

from itertools import groupby
from operator import itemgetter

logs = [('2009-09-02', 11),
          ('2009-09-02', 3),
          ('2009-09-03', 10),
          ('2009-09-03', 4),
          ('2009-09-03', 22),
          ('2009-09-06', 33),
          ('2009-09-02', 13),
          ('2009-09-03', 15)]

for key, entries in groupby(sorted(logs), itemgetter(0)): # Group by 1st element in tuple
    print key, sum(entry[1] for entry in entries) # Sum 2nd element in tuple