Python List Comprehension: assign to multiple variables

Question

Is there a way to assign to multiple variables in a one-liner?

Let's say I have a list of 3D points and I want x, y and z lists.

polygon = [(0, 0, 0), (1, 0, 0), (1, 1, 0), (0, 1, 0)]
# this works to get the expected result, but is not a single list comprehension
x = [x for x, y, z in polygon ]
y = [y for x, y, z in polygon ]
z = [z for x, y, z in polygon ]

I am thinking of something like:

x, y, z = [... for x, y, z in polygon ]

• DirtyBit: look for zip(*polygon)?

Answer 1

You can use zip() function:

polygon = [(0, 0, 0), (1, 0, 0), (1, 1, 0), (0, 1, 0)]
x, y, z = zip(*polygon)
print(x)
print(y)
print(z)

Prints:

(0, 1, 1, 0)
(0, 0, 1, 1)
(0, 0, 0, 0)

---

Or if you want lists instead of tuples:

x, y, z = map(list, zip(*polygon))

Answer 2

Unpack the list of tuples using zip():

polygon = [(0, 0, 0), (1, 0, 0), (1, 1, 0), (0, 1, 0)]
x,y,z = zip(*polygon)
print(list(x))
print(list(y))
print(list(z))

OUTPUT:

[0, 1, 1, 0]
[0, 0, 1, 1]
[0, 0, 0, 0]

EDIT:

If you want the lists:

x,y,z = [list(a) for a in zip(*polygon)]