Python Ternary Elif

Summary: To use an elif branch in the ternary operator, use another ternary operator as the result of the else branch (nested ternary operator). The nested ternary operator x if c0 else y if c1 else z returns x if condition c0 is met, else if (elif) condition c1 is met, it returns y, else it returns z.

Python Ternary Elif

Problem: You may have seen the ternary operator x if c else y. Is there a similar ternary operator with an additional elif statement? In pseudocode, you want something like:

# Pseudocode
x if c elif y0 else y1

In other words: What’s the best way of extending the ternary operator to what you may call a “quaternary” operator?

Background: The most basic ternary operator x if c else y consists of three operands x, c, and y. It is an expression with a return value. The ternary operator returns x if the Boolean expression c evaluates to True. Otherwise, if the expression c evaluates to False, the ternary operator returns the alternative y.

Learn more about the ternary operator in our detailed blog article!

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

>>> x = 42
>>> if x > 42:
>>>     print("no")
>>> elif x == 42:
>>>     print("yes")
>>> else:
>>>     print("maybe")
yes

The elif branch wins: you 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):

Method: Nested Ternary Operator

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

>>> print("no") if x > 42 else print("yes") if x == 42 else print("maybe")
yes

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!

Try it yourself:

Exercise: Which method is more concise? Count the number of characters (or write a small script that does it for you ;))!

Python Ternary Multiple Elif

In the previous example, you’ve seen how a nested ternary operator semantically adds an elif branch. In theory, you can add an arbitrary number of elif branches by nesting more and more ternary operators:

# Method 1: If ... Elif ... Else
x = 42
if x > 42:
    y = 1
elif x == 42:
    y = 2
elif x == 12:
    y = 3
else:
    y = 4
print(y)
# 2

# Method 2: Nested Ternary Operator
y = 1 if x > 42 else 2 if x == 42 else 3 if x == 12 else 4
print(y)
# 2

However, readability suffers badly and you shouldn’t do anything of the sort. A simple mult-line if ... elif ... elif ... else statement is better!

Discussion

However, even if the nested ternary operator is more concise than an if-elif-else statement, it’s not recommended because of readability of your code. Most programmers don’t have any trouble understanding a simple if-elif-else statement. But a nested ternary operator is an advanced-level piece of Python code and especially beginners will struggle understanding it.

So, it’s great that you’ve expanded your One-Liner Superpower. But you should use it wisely!

Related Video: If-Then-Else in One Line of Python Code

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