Best run of days

Daily profits can be negative. Find the largest total over any run of consecutive days (at least one day). One method: walk the days keeping a running total of the current run. For each day, in this order: add the day to the running total; if the running total is now the best seen so far, remember it; then, if the running total is below zero, reset it to zero, because a negative run can only hurt whatever comes next. Because a run must have at least one day, start best at the first day's profit, not at zero, so that an all-negative list still gives the least bad day.

Write best_run(profits) for a non-empty list.

best_run([-2, 1, -3, 4, -1, 2, 1, -5, 4])  ->  6     (4 - 1 + 2 + 1)
best_run([-3, -1, -2])                     ->  -1

def best_run(profits):
    ...