Stop Using ‘or’ to Test Multiple Values Against a Variable in Python

Stop Using “or” to Test Multiple Values Against a Variable in Python

Use the “in” keyword for multiple comparisons

If you’ve ever needed to check that a variable is equal to one of many possible values, you’ve probably written something like this:if x == 1 or x == 10 or x == 100:
 pass

Well, there’s a better way!

Let’s go through how to use the in keyword instead of or to recreate the expression above.

What is the “in” Keyword?

The keyword in can be used to search through a sequence and will return either True or False depending on whether the left operand is found.

Here’s a simple example, checking for the letter e in a string:result = 'e' in 'The'
print(result) # True

Since the in keyword can be used with any sequence, we place all the values that we’re comparing with our variable into a single sequence. The question is now, which data type is best?

The initial response may be to use a list:if x in [1,10,100]:
 pass

This works fine, although we can squeeze better performance out by using a tuple or even a set:# tuple example
if x in (1,10,100):
 pass# set example
if x in {1,10,100}:
 pass

Using the in keyword is not only less syntax to initially type, it’s easier to read and maintain. Feel free to create your tuple on a separate line and use it in the if statement, to keep your code more readable.matches = (1,10,100)if x in matches:
 pass

Remember, this technique is only appropriate for equality comparisons. However, you can invert the expression to effectively test for inequality:if x not in (1,10,100):
 pass

When simple becomes overbearing, find ways to write code that are more concise, easy to read, and maintainable.

I hope this was helpful, share your thoughts and comments below!