解包未指定数量的变量

Question

So I have a list of tuples. Each tuple in the list will be the same length, but tuple size will vary based on list. For example, one list could contain tuples of length 4, another could contain tuples of length 5. I want to unpack each individual value of a tuple, and use each value to multiply it by an element in another list. For example(with a list of tuples of length 3):

somelist = [a,b,c]
tuplelist = [(2,3,5),(5,7,5),(9,2,4)]
listMult = []
for x,y,z in tuplelist:
    listMult.append([somelist[0]*x,somelist[1]*y,somelist[2]*z])

The problem with this is that it won't scale if I'm using another list with tuples of a different size.

Answer 1

If you don't know how many elements each tuple has, unpacking would be a bad idea. In your example, you would instead do the following:

listMult = [sum(x*y for x, y in zip(tup, somelist)) for tup in tuplelist]

In general, you'd try to use iteration, starargs, and other things that operate on an iterable directly instead of unpacking.

Answer 2

As presented, the question is incompletely specified. But there is an interesting and useful variant of the question, "How do I unpack a fixed number of elements from tuples of an unknown length?".

The answer to that might be useful to you:

tuple_list = [(2,3), (5,7,5), (9,2,4,2)]
pad_tuple = (0, 0, 0)
for t in tuple_list:
    t += pad_tuple             # make sure the tuple is sufficiently long
    x, y, z = t[:3]            # only extract the first three elements
    print(x,y,z)