maximum subarray of currency usd to rub for 5 years

usd_rub.py

import csv

def find_crossing(a, low, mid, high):
	max_left = 0
	max_right = 0

	left_sum = -1e308
	sum = 0
	for i in range(mid, low, -1):
		sum = sum + a[i][1]
		if sum > left_sum:
			left_sum = sum
			max_left = i
			max_right = 0

	right_sum = -1e308
	sum = 0
	for j in range(mid + 1, high):
		sum = sum + a[j][1]
		if sum > right_sum:
			right_sum = sum
			max_right = j

	return max_left, max_right, left_sum + right_sum


def find_max_subarray(a, low, high):
	if high == low:
		return low, high, a[low][1]
	else:
		mid = (low + high) / 2

		left_low, left_high, left_sum = find_max_subarray(a, low, mid)
		right_low, right_high, right_sum = find_max_subarray(a, mid + 1, high)
		cross_low, cross_high, cross_sum = find_crossing(a, low, mid, high)

		if (left_sum >= right_sum) & (left_sum >= cross_sum):
			return left_low, left_high, left_sum
		elif (right_sum >= left_sum) & (right_sum >= cross_sum):
			return right_low, right_high, right_sum
		else:
			return cross_low, cross_high, cross_sum

courses = []

reader = csv.reader(open('data.csv', 'rb'), delimiter=',', quotechar='"')
prev = 0
for row in reader:
	cur = float(row[1])
	if prev == 0:
		prev = cur 
	value = [row[0], prev - cur, row[1]]
	prev = cur
	courses.insert(0, value)

min, max, sum = find_max_subarray(courses, 0, len(courses)-1)

print courses[min]
print courses[max]
print sum