from itertools import groupby
from operator import itemgetter
def summary(data, key=itemgetter(0), value=itemgetter(1)):
"""Summarise the supplied data.
Produce a summary of the data, grouped by the given key (default: the
first item), and giving totals of the given value (default: the second
item).
The key and value arguments should be functions which, given a data
record, return the relevant value.
"""
for k, group in groupby(data, key):
yield (k, sum(value(row) for row in group))
if __name__ == "__main__":
# Example: given a set of sales data for city within region,
# produce a sales report by region
sales = [('Scotland', 'Edinburgh', 20000),
('Scotland', 'Glasgow', 12500),
('Wales', 'Cardiff', 29700),
('Wales', 'Bangor', 12800),
('England', 'London', 90000),
('England', 'Manchester', 45600),
('England', 'Liverpool', 29700)]
for region, total in summary(sales, key=itemgetter(0), value=itemgetter(2)):
print "%10s: %d" % (region, total)
