How to Efficiently Test Multiple Variables for Equality Against a Single Value in Python?

How to Simultaneously Test Multiple Variables for Equality against a Single Value in Python

When comparing numerous variables to an integer and generating a three-letter string as output, you may encounter challenges translating this concept into Python. Let's delve into the issue and find the most efficient solution.

Consider the following code snippet:

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 of this code should be:

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

However, due to the nature of boolean expressions, Python evaluates each side of the or operator separately. Consequently, this code will not produce the desired result.

To resolve this issue, you can employ an alternative approach, such as testing each variable individually against the specific value:

if x == 1 or y == 1 or z == 1:
    mylist.append("d")

Alternatively, you can utilize a containment test against a tuple or a set:

if 1 in (x, y, z):
    mylist.append("d")

# Or even more efficiently
if 1 in {x, y, z}:
    mylist.append("d")

Sets offer constant-cost membership testing, making them an optimal choice for this scenario.

It's crucial to remember that boolean expressions follow a hierarchy of operations, with operators like or having a lower precedence than comparison operators like ==. Understanding these precedence rules will help you write more effective and precise code.

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