Recover the sequence

#!/usr/bin/env python
import sys
from multiprocessing import Pool

def time_function(func):
    def wrapped_func(*args, **kwargs):
        from time import time
        start = time()
        sys.stderr.write('Function %s started\n' % (func.__name__,))
        res = func(*args, **kwargs)
        sys.stderr.write('Function %s finished in %.6fs\n' % (func.__name__, time() - start))
        return res
    return wrapped_func

class Problem(object):
    def __init__(self, data):
        self.length, self.seq = data
        self.length = int(self.length)
        self.seq = list(self.seq)

    def checksum(self, arr):
        result = 1
        for i in range(len(arr)):
            result = (31 * result + arr[i]) % 1000003
        return result

    def reversed_merge_sort(self, arr):
        n = len(arr)
        if n <= 1:
            return arr

        mid = n / 2
        first_half = self.reversed_merge_sort(arr[:mid])
        second_half = self.reversed_merge_sort(arr[mid:])
        return self.merge(first_half, second_half)

    def merge(self, arr1, arr2):
        result = []
        while len(arr1) > 0 and len(arr2) > 0:
            s = self.seq.pop(0)
            if s == '1':
                result.append(arr1.pop(0))
            else:
                result.append(arr2.pop(0))
        result += arr1
        result += arr2
        return result

    @time_function
    def get_solution(self):
        result = [0] * self.length
        for i, res in enumerate(self.reversed_merge_sort(range(self.length))):
            result[res] = i + 1
        return self.checksum(result)


@time_function
def main():
    input_file = open('input.txt')
    data = input_file.read().split()
    n = int(data.pop(0))
    results = {}
    pool = Pool()
    for i in range(1, n + 1):
        args = data.pop(0), data.pop(0)
        results[i] = pool.apply_async(Problem(args).get_solution)
    pool.close()
    pool.join()

    for i in sorted(results):
        print "Case #%d: %s" % (i, results[i].get())

if __name__ == '__main__':
    from doctest import testmod
    print >> sys.stderr, testmod()
    main()