python decompose a list

Question

I remember I once seen a operator which is able to decompose a list in python.

for example

[[1],[2],[3]]

by applying that operator

Answer 1

The correct answer to the OP's question: "what is that operator" which transforms the list [[1],[2],[3]] to [1], [2], [3] is tuple() since [1], [2], [3] is a tuple. The builtin function tuple will convert any sequence or iterable to a tuple, although there is seldom a need to do so since, as already pointed out, unpacking a list is as easy as unpacking a tuple:

a, b, c = [[1],[2],[3]]

gives the same result as

a, b, c = tuple([[1],[2],[3]])

This may not be what the OP wanted but it is the correct answer to the question as asked.

Answer 2

If you want to pass a list of arguments to a function, you can use *, the splat operator. Here's how it works:

list = [1, 2, 3]
function_that_takes_3_arguments(*list)

If you want to assign the contents of a list to a variable, you can list unpacking:

a, b, c = list # a=1, b=2, c=3

Answer 3

This can be achieved by running sum(list_name,[]) as mentioned here.

You may also find this question on flattening shallow lists relevant.

Answer 4

You can use the tuple function to convert a list to a tuple. A tuple with three elements isn't really any different from three separate elements, but it gives a handy way to work with all three together.

li = [[1], [2], [3]]
a, b, c = tuple(li)
print a  # [1]