Python 3: Variable Scoping

Question

def max_sum_subarray(arr):
    cur_max_sum = global_max_sum = arr[0]
    start = end = 0

    sz = len(arr)
    for i in range(1, sz):
        cur_max_sum = max(arr[i], cur_max_sum+arr[i])
        global_max_sum = max(global_max_sum, cur_max_sum)
        if cur_max_sum > global_max_sum:
            global_max_sum = cur_max_sum
            end = i
    g = global_max_sum

    for i in range(end, -1, -1):
        g -= arr[i]
        if not g:
            start = i
            break

    ans = {
        'global_max_sum': global_max_sum,
        'start': start+1,
        'end': end+1
    }
    return ans

Here, start and end don't get updated inside for loop under if, though the condition satisfies. If start or end is used out of if, there is no problem with it. Is there any scoping problem or something else? Please explain me in details.

Thanks in advance.

Answer 1

It's a logic error:

global_max_sum = max(global_max_sum, cur_max_sum)
if cur_max_sum > global_max_sum:

There's literally no way for cur_max_sum to be greater than global_max_sum.