A small depiction of issues with floating point arithmetic in python.

gistfile1.txt

def naive_add(lis):
    total = 0
    for elem in lis:
        total += elem
    return total

def recursive_add(lis):
    if len(lis) == 1:
        return lis[0]
    elif len(lis) == 0:
        return 0
    else:
        mid = len(lis)/2
        return recursive_add(lis[:mid]) + recursive_add(lis[mid:])

def generate_big_list_of_smalls():
    mylist = [1000000000]+[.0001]*10000000
    # 1,000,000,000
    # .0001 * 10,000,000 = 1,000
    print "list generated"
    return mylist

def test_adding(mylist):
    nsum = naive_add(mylist)
    rsum = recursive_add(mylist)
    psum = sum(mylist)

    print "naive:", nsum
    print "recursive", rsum
    print "built-in", psum

li = generate_big_list_of_smalls()
test_adding(li)

# ⚲python floating_math.py 
# list generated
# naive:     1000001000.17
# recursive: 1000001000.0
# built-in:  1000001000.17