python conditional assignment one line

One line if without else in Python

by Nathan Sebhastian

Posted on Feb 22, 2023

Reading time: 4 minutes

If you don’t have an else statement, then you can write a one line if statement in Python by removing the line break as follows:

There are 3 different ways you can create a one line if conditional without an else statement:

• The regular if statement in one line
• Using the ternary operator syntax
• Shorthand syntax with the and operator

This tutorial shows you examples of writing intuitive one line if statements in practice.

1. One line if statement

In the following example, the if statement prints something if x value is greater than 10 :

Now here’s how you convert the code into one line if statement:

Yup! Just remove the line break and you’re good to go.

If you have more than one line in the if body, you can use a semicolon to mark the end of the statements. See the example below:

But keep in mind that this code violates Python coding conventions by defining multiple statements in one line.

It’s also harder to read when you have complex statements inside the if body. Still, the code works well when you have simple conditionals.

2. Ternary operator syntax without else

The Python ternary operator is used to create a one line if-else statement.

It comes in handy when you need to write a short and simple if-else statement as follows:

You can read this article to learn more about how ternary operators work in Python.

You can use the ternary operator to write a one line if statement without an else as follows:

By returning None , Python will do nothing when the else statement is executed.

Although this one line if statement works, it’s not recommended when you have an assignment in your if body as follows:

Using the ternary operator, you still need to assign the original value of y in the else statement as follows:

The ternary operator doesn’t allow you to discard the else statement, so this code redundantly assigns the value of y to y in the else statement.

It’s better to use a regular if statement as follows:

Using a regular if statement has less repetition and easier to read.

3. Shorthand syntax with the and operator

The and operator can be used to shorthand an if statement because this operator executes the second operand only when the first operand returns True .

Suppose you have an if statement as follows:

You can use the and operator to rewrite the code above as follows:

The print() function above is only executed when the expression on the left side of the and operator returns True .

But this method also falls short when you need to do an assignment as it will raise an error:

If your conditional involves an assignment, then you need to use the regular if statement.

This tutorial has shown you examples of writing a one line if without else statement in Python.

In practice, writing a one line if statement is discouraged as it means you’re writing at least two statements in one line: the condition and the code to run when that condition is True .

Just because you can, doesn’t mean you should. Writing a regular if statement with line breaks and indents provides you with a clean and consistent way to define conditionals in your code.

I hope this tutorial helps. Happy coding! 👍

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If-Then-Else in One Line Python

Quick answer : How to put a simple if-then-else statement in one line of Python code?

To put an if-then-else statement in one line, use Python’s ternary operator x if c else y . This returns the result of expression x if the Boolean condition c evaluates to True . Otherwise, the ternary operator returns the alternative expression y .

While you read through the article to boost your one-liner power, you can listen to my detailed video explanation:

Here’s another minimal example where you return 21 if the condition 3>2 evaluates to True , otherwise, you return 42 :

The output 42 is stored in the variable var .

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So the natural question arises: can you write conditional if-then-else statements in a single line of code?

This article explores this mission-critical question in all detail.

Can you write the if-then-else statement in a single line of code?

Yes, you can write most if statements in a single line of Python using any of the following methods:

• Write the if statement without else branch as a Python one-liner: if 42 in range(100): print("42") .
• If you want to set a variable, use the ternary operator : x = "Alice" if "Jon" in "My name is Jonas" else "Bob" .
• If you want to conditionally execute a function, still use the ternary operator : print("42") if 42 in range(100) else print("21") .

In the previous paragraph, you’ve unwillingly learned about the ternary operator in Python.

The ternary operator is something you’ll see in most advanced code bases so make sure to understand it thoroughly by reading the following section of this article.

I drew this picture to show visually how the ternary operator works:

Let’s dive into the three different ways to write the if-then-else statement as a Python one-liner .

Related articles : Python One Line Ternary

How to Write the If-Then-Else Statement as a Python One-Liner?

Let’s have a look at all the ways how you can write the if-then-else statement in one line.

The trivial answer is to just write it in one line—but only if you don’t have an else branch:

Case 1: You Don’t Have an Else Branch

Consider the following code snippet where you check for the number 42 whether it falls in a range of numbers:

This code snippet will indeed print the output because the integer 42 falls into the range of numbers from 0 to 99.

But how can we write this if statement in a single line of code?

Just use a single line like this:

The two statements are identical so this is the way to do it—if you can write the conditional body in a single line of code.

However, if you try to become too fancy and you use a nested if body, it won’t work:

Python cannot handle this anymore: the interpreter throws an “invalid syntax” error because the statement became ambiguous.

But don’t worry, there’s a workaround: the ternary operator .

Case 2: You Have an Else Branch And You Want to Conditionally Assign a Value

In case you have an else branch and you want to conditionally assign a value to a variable, the ternary operator is your friend.

Say, you want to write the following if-then-else statement in a single line of code:

As the string "Jon" appears in the string "My name is Jonas" , the variable x will take value "Alice" .

Can we write it in a single line? Sure—by using the ternary operator .

The ternary operator is very intuitive. Just read it from left to right and you’ll understand its meaning.

We assign the value "Alice" to the variable x in case the following condition holds: "Jon" in "My name is Jonas" . Otherwise, we assign the string "Bob" to the variable x .

Ternary Operator Syntax : The three operands are written as x if c else y which reads as “return x if c else return y “. Let’s write this more intuitively as:

Case 3: What If You Don’t Want to Assign Any Value But You Have an Else Branch?

Well, there’s a quick and dirty hack: just ignore the return value of the ternary operator.

Say, we want to compress the following if-then-else statement in a single line of code:

The problem is that we don’t have a return value. So can we still use the ternary operator?

As it turns out, we can. Let’s write this if-then-else statement in a single line:

We use the ternary operator. The return value of the print() function is simply None . But we don’t really care about the return value, so we don’t store it in any variable.

We only care about executing the print function in case the if condition is met.

How to Write an If-Elif-Else Statement in a Single Line of Python?

In the previous paragraphs, you’ve learned that we can write the if-else statement in a single line of code.

But can you one-linerize an elif expression with multiple conditions?

Of course, you can!

(Heuristic: If you’re in doubt about whether you can do XYZ in a single line of Python, just assume that you can. See here .)

Say, you want to write the following if-then-else condition in a single line of code:

The elif branch wins! We print the output "yes" to the shell.

But how to do it in a single line of code? Just use the ternary operator with an elif statement won’t work (it’ll throw a syntax error).

The answer is simple: nest two ternary operators like so:

If the value x is larger than 42 , we print "no" to the shell.

Otherwise, we execute the remainder of the code (which is a ternary operator by itself). If the value x is equal to 42 , we print "yes" , otherwise "maybe" .

So by nesting multiple ternary operators, we can greatly increase our Python one-liner power!

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Related Questions

Let’s quickly handle a bunch of related questions:

How to Write If Without Else in One Line?

We’ve already seen an example above: we simply write the if statement in one line without using the ternary operator: if 42 in range(100): print("42") .

Python is perfectly able to understand a simple if statement without an else branch in a single line of code.

How to Write Elif in One Line?

We cannot directly write the elif branch in one line of Python code. But we can nest two ternary operators instead:

Python If-Else One-Liner: What Does It Return?

The ternary operator always returns the result of the conditional evaluation. Again, the code snippet 100 if x>42 else 42 returns the integer value 42.

If you only execute functions within the ternary operator, it’ll return the None value.

Related Video Tutorial

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Where to Go From Here

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