solution to max sub array problem in python

maxsub.py

def maxSubArray(ls):
    if len(ls) == 0:
       raise Exception("Array empty") # should be non-empty
      
    runSum = maxSum = ls[0]
    i = 0
    start = finish = 0

    for j in range(1, len(ls)):
    	if ls[j] > (runSum + ls[j]):
            runSum = ls[j]
            i = j
        else:
            runSum += ls[j]

        if runSum > maxSum:
            maxSum = runSum
            start = i
            finish = j

    print "maxSum =>", maxSum
    print "start =>", start, "; finish =>", finish

maxSubArray([-2, 11, -4, 13, -5, 2])
maxSubArray([-15, 29, -36, 3, -22, 11, 19, -5])

It does not work as expected...
In the first case it should return 13 instead of 11

An easier approach has been mentioned on the Wikipedia page