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
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:
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
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
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!
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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