how to handle an empty list, python3

I have a function that creates a list of aminoacids (aaCandidates), but this list can even be empty. If this list is empty I would like to jump the step and continue with the following one.

My code is:

def magicfunction(referenceDistance,referenceAA):

    amminoacids = ('A', 'R', 'N', 'D', 'C', 'Q', 'E', 'G', 'H', 'I', 'L', 'K', 'M', 'F', 'P', 'S', 'T', 'W', 'Y', 'V')
    aaCandidates = list()
    for aa in amminoacids:
        if distance(aa,referenceAA) == referenceDistance:
            aaCandidates.append(aa)
        if not aaCandidates:
            break

    luckyAA = choice(aaCandidates)

    return(luckyAA)

I call this function in another file as follow:

for i in range(lenghtPairs):
    r1 = randrange(20)
    r2 = randrange(20)
    coppie.append([aminoacidi[r1], aminoacidi[r2]])

for i in range(lenghtPairs):
    dictionary = dict()
    frequenze = dict()

    if i == 0:
        a = randrange(20)
        b = randrange(20)
        pairs[0] = [aminoacids[a], aminoacids[b]]
    else:
        c = randrange(20)
        pairs[i][0] = aminoacids[c]
        distanceNeighbours = distance(pairs[i][0],pairs[i-1][0])
        aaChosen = magicfunction(distanceNeighbours,pairs[i-1][1])
        pairs[i][1] = aaChosen

    print(i + 1)

I tried the condition => if not aaCandidates: break but it didn't work.