Mutating a List Doesn't Need nonlocal, Rebinding Does

def make_tracker():
    log = []
    total = 0
    def record(x):
        log.append(x)
        total += x
        return total
    return record, log

track, log = make_tracker()
track(5)

Now compare with this version, where the only change is one added line inside record:

def make_tracker():
    log = []
    total = 0
    def record(x):
        nonlocal total
        log.append(x)
        total += x
        return total
    return record, log

track, log = make_tracker()
track(5)

What happens in each case?