How to end loop one iteration earlier?

Question

I often need to end loop one iteration earlier, how do I do it elegantly? Breaking out of nested loops looks messy to me. For now I workaround it with return, but when later on I want to make a class, having return in the middle of constructor looses sense.

def forward(neurons):
for layerId, layer in enumerate(neurons):
    if layerId == neurons.__len__() - 1:
        return
    for idx, i in enumerate(neurons[layerId]):
        for idx2, n in enumerate(neurons[layerId+1]):
            neurons[layerId+1][idx2] += i * sigmoid(weights[layerId][idx][idx2])

Answer 1

One generic solution would be to create a generator from the iterator (that will yield all but the last element the iterator yields):

def but_last(p):
    first = True
    for x in p:
        if not first:
            yield last
        first = False
        last = x

for layerId, layer in but_last(enumerate(neurons)):
    do_your_stuff(layerId, layer)