# How to test multiple variables against a value?

### Question

I'm trying to make a function that will compare multiple variables to an integer and output a string of three letters. I was wondering if there was a way to translate this into Python. So say:

``````x = 0
y = 1
z = 3
mylist = []

if x or y or z == 0 :
mylist.append("c")
if x or y or z == 1 :
mylist.append("d")
if x or y or z == 2 :
mylist.append("e")
if x or y or z == 3 :
mylist.append("f")
``````

which would return a list of

``````["c", "d", "f"]
``````

Is something like this possible?

1
578
2/4/2019 8:55:29 AM

You misunderstand how boolean expressions work; they don't work like an English sentence and guess that you are talking about the same comparison for all names here. You are looking for:

``````if x == 1 or y == 1 or z == 1:
``````

`x` and `y` are otherwise evaluated on their own (`False` if `0`, `True` otherwise).

You can shorten that using a containment test against a tuple:

``````if 1 in (x, y, z):
``````

or better still:

``````if 1 in {x, y, z}:
``````

using a `set` to take advantage of the constant-cost membership test (`in` takes a fixed amount of time whatever the left-hand operand is).

When you use `or`, python sees each side of the operator as separate expressions. The expression `x or y == 1` is treated as first a boolean test for `x`, then if that is False, the expression `y == 1` is tested.

This is due to operator precedence. The `or` operator has a lower precedence than the `==` test, so the latter is evaluated first.

However, even if this were not the case, and the expression `x or y or z == 1` was actually interpreted as `(x or y or z) == 1` instead, this would still not do what you expect it to do.

`x or y or z` would evaluate to the first argument that is 'truthy', e.g. not `False`, numeric 0 or empty (see boolean expressions for details on what Python considers false in a boolean context).

So for the values `x = 2; y = 1; z = 0`, `x or y or z` would resolve to `2`, because that is the first true-like value in the arguments. Then `2 == 1` would be `False`, even though `y == 1` would be `True`.

The same would apply to the inverse; testing multiple values against a single variable; `x == 1 or 2 or 3` would fail for the same reasons. Use `x == 1 or x == 2 or x == 3` or `x in {1, 2, 3}`.

756
3/12/2018 7:56:00 PM

``````x = 0