[Tut] Python One Line If Without Else

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Python One Line If Without Else

Crafting beautiful Python one-liners is as much an art as it is a science. In this tutorial, you’ll learn how to compress an if statement without an else branch into a single line of Python code.



Problem: What’s the one-liner equivalent of the simple if statement without an else branch?

Here’s an example:

Code:

condition = True if condition: print('hi') # hi

You may want to (i) print something, (ii) assign a value to a variable, or (iii) append an element to a list if the condition holds.

In this article, I’ll show you four methods of how to accomplish this goal. All four methods are generally applicable—and you can easily customize them to your specific application.

Let’s have a quick overview of the four methods in our interactive code shell:

https://trinket.io/embed/python/02d2d186a2

Exercise: Run the code for both

Code:

True

and

Code:

False

conditions. Are all methods semantically equivalent?

Method 1: One-Liner If Statement

The first is also the most straightforward method: if you want a one-liner without an else statement, just write the if statement in a single line! There are many tricks (like using the semicolon) that help you create one-liner statements. But for an if body with only one statement, it’s just as simple as avoiding the line break.

Code:

condition = True # Method 1: One-Liner If if condition: print('hi') # hi

This method is perfectly valid and you could see it in practice. Yet, I have to mention that it “violates” the PEP8 standard (multiple statements in a single line). Therefore, you shouldn’t consider this to be Pythonic code (there are worse things under the sun though).

Method 2: Ternary with Throw-Away Else Branch

Sure, you can also use the ternary operator:



If you need a quick refresher on the ternary operator, check out my detailed blog article.The ternary operator is commonly used to conditionally assign values. But you can also throw away the return value by not assigning the result to any variable. In this case, it doesn’t matter if you use

Code:

None

or any other “dummy” return value as the result of the else branch:

Code:

condition = True # Method 2: Ternary with Dummy print('hi') if condition else None

It’s readable, short, and concise and I like this (well, I may be a bit biased as author of the book Python One-Liners). Sure, people will ask why you didn’t write it in multiple lines. But where is the fun there?

Method 3: Ternary with Default Value for Assignment

If you need to assign a value conditionally to a variable, but you want to do so without an else branch, you can do the following:

Code:

condition = True # Method 3: Ternary with Dummy for Assignment x = 42 if condition else None

If the condition does not hold, the “dummy” value

Code:

None

is assigned to the variable.

Method 4: Short Circuiting

This method I like most. It uses a Python optimization called “short circuiting” for Boolean operators: the logical

Code:

and

operator simply returns the second operand if the first is

Code:

True

. There’s no Boolean conversion of the second operand, it’s just returned as is.

If the first operand is

Code:

False

, the second operand is not even evaluated.

You can use this to conditionally execute the if branch

Code:

print('hi')

or any other code function.

Code:

condition = True # Method 4: Short circuiting condition and print('hi')

There are two options:

• Code:

  condition == True
  : As the first operand is
  Code:

  True
  , the second operand is returned. Thus, the statement
  Code:

  print('hi')
  is executed and the string
  Code:

  hi
  appears on the screen.
  
  
• Code:

  condition == False
  : As the first operand is
  Code:

  False
  , the second operand is not even evaluated because the result of the logical
  Code:

  and
  operation is
  Code:

  False
  anyway. Thus, the statement
  Code:

  print('hi')
  is never executed.
  

Where to Go From Here?

Enough theory, let’s get some practice!

To become successful in coding, you need to get out there and solve real problems for real people. That’s how you can become a six-figure earner easily. And that’s how you polish the skills you really need in practice. After all, what’s the use of learning theory that nobody ever needs?

Practice projects is how you sharpen your saw in coding!

Do you want to become a code master by focusing on practical code projects that actually earn you money and solve problems for people?

Then become a Python freelance developer! It’s the best way of approaching the task of improving your Python skills—even if you are a complete beginner.

Join my free webinar “How to Build Your High-Income Skill Python” and watch how I grew my coding business online and how you can, too—from the comfort of your own home.

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