How to Test Multiple Variables for Equality Against a Single Value

How to test multiple variables for equality against a single value?

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 (i.e. in takes a fixed amount of time whatever the left-hand operand is).

Explanation

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}.

What's the prettiest way to compare one value against multiple values?

Don't try to be too sneaky, especially when it needlessly affects performance.
If you really have a whole heap of comparisons to do, just format it nicely.

if (foobar === foo ||
    foobar === bar ||
    foobar === baz ||
    foobar === pew) {
     //do something
}

Check if multiple variables have the same value

If you have an arbitrary sequence, use the all() function with a generator expression:

values = [x, y, z]  # can contain any number of values
if all(v == 1 for v in values):

otherwise, just use == on all three variables:

if x == y == z == 1:

If you only needed to know if they are all the same value (regardless of what value that is), use:

if all(v == values[0] for v in values):

or

if x == y == z:

Compare to multiple values in an if statement

Use the in operator

if num in a : 

as in

def test(num): 
    a = [1, 2, 3]
    if num in a : 
        return True
    else : 
        return False

a work around would be (as suggested by Padraic)

 def test(num): 
        a = [1, 2, 3]
        return num in a

This would work because, The in operator compares if the LHS is present in the RHS and returns a boolean value respectively.

Also this is possible

test = lambda x:  num in [1, 2, 3]

That is all in a single line!

How to compare multiple variables to the same value?

You want to test a condition for all the variables:

if all(x >= 2 for x in (A, B, C, D)):
    print(A, B, C, D)

This should be helpful if you're testing a long list of variables with the same condition.

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If you needed to check:

if A, B, C, or D >= 2:

Then you want to test a condition for any of the variables:

if any(x >= 2 for x in (A, B, C, D)):
    print(A, B, C, D)

How can I check whether multiple variables are equal to the same value?

if((A == 'X' || A == 'O') && A == B && B == C)
{
    // Do whatever
}

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