How to Efficiently Compare Multiple Python Variables to a Single Integer Value?

Comparing Multiple Variables to a Single Value

Problem Description:

Seeking a method in Python to ascertain whether multiple variables are equal to a particular integer and subsequently produce a string composed of three letters. For instance, given:

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")

...the expected output would be a list of ["c", "d", "f"].

Answer:

The provided code misunderstands Boolean expressions in Python. The or operator examines each side separately, resulting in the following evaluation:

(x == False or y == False) or (y == False or z == False)

To verify that at least one variable equals the desired integer, use the following expression:

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

Alternatively, for improved efficiency:

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

Explanation:

Operators have precedence in Python, and the or operator has lower precedence than equality (=). Therefore, equality is evaluated first. Moreover, the or operator returns the first truthy value encountered. This means that the code sequence:

x or y or z == 0

would return False if x was not 0, even if y or z was. To evaluate multiple variables against a single value correctly, use an expression such as:

x == 1 or y == 1 or z == 1

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