deltas.py

import operator
import copy

todays = range(10)
yesterdays = copy.copy(todays)[1:]

# todays =     [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
# yesterdays = [1, 2, 3, 4, 5, 6, 7, 8, 9]

# now pair up a today with a yesterday...
todays_and_yesterdays = zip(todays, yesterdays)

# todays_and_yesterdays = [(0, 1), (1, 2), (2, 3), (3, 4), (4, 5), (5, 6), (6, 7), (7, 8), (8, 9)]

# ...and subtract!
deltas = map(lambda the_day_and_before: operator.sub(*the_day_and_before), todays_and_yesterdays)

# deltas = [-1, -1, -1, -1, -1, -1, -1, -1, -1]