Python swapping lists

Question

In python, when I assign a list to another, like:

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

Now b and a point to the same list. Now considering two lists,

Answer 1

Because Python assignment first evaluates the right-hand-side expression, then applies the result to the left-hand-side targets.

So, first, Python creates (, ) as a tuple, then assigns the first item in that tuple to a, and the second item in that tuple to b. This swaps the references around neatly.

You could expand the assignment to read it like this:

tmp = b, a
a = tmp[0]
b = tmp[1]