Swapping 1 with 0 and 0 with 1 in a pythonic way?

Question

In some part of my Python program I have a val variable that can be 1 or 0. If it's 1 I must change to 0, if it's 0 I must change to 1.

How do you do it in a Pythonic way?

if val == 1:
    val = 0
elif val == 0:
    val = 1

it's too long!

I did:

swap = {0: 1, 1:0}

So I can use it:

swap[val]

Other ideas?

Answer 1

This isn't pythonic, but it is language neutral. Often val = 1 - val is simplest.

Answer 2

Since True == 1 and False == 0 in python,

you could just use var = not var

It will just swap it.

Answer 3

If you want to be short:

f = lambda val: 0 if val else 1

Then:

>>> f(0)
1
>>> f(1)
0

Answer 4

In your case I recommend the ternary:

val = 0 if val else 1

If you had 2 variables to swap you could say:

(a, b) = (b, a)

Answer 5

Just another possibility:

i = (1,0)[i]

The advantage is that it generates an error if i is anything else than 0 or 1.

Are you sure you don't want to use False and True? It sounds almost like it.

Answer 6

The shortest is the bitwise operator XOR:

val ^= 1