[Tut] Python Ternary — Tuple Syntax Hack

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Python Ternary — Tuple Syntax Hack

You may know the ternary operator

Code:

x if c else y

in Python which reads as “return

Code:

x

if

Code:

c

else return

Code:

y

“. But you may not know that you can also write the ternary operator in a shorter form as

Code:

(y, x)[c]

. Let’s dive into this concise way of hacking your own ternary operator!



A shorthand form of the ternary operator is the following tuple syntax hack.

Syntax: You can use the tuplesyntax

Code:

(x, y)[c]

consisting of a tuple

Code:

(x, y)

and a condition

Code:

c

enclosed in a square bracket. Here’s a more intuitive way to represent this tuple syntax.

Code:

(<OnFalse>, <OnTrue>)[<Condition>]

Operand |
Description

|
The return expression of the operator in case the condition evaluates to

Code:

True

|
The condition that determines whether to return the or the branch.

|
The return expression of the operator in case the condition evaluates to

Code:

False

[i]Tuple Syntax of the Ternary Operator[/i]

https://trinket.io/embed/python/8b1118a41c

Exercise: Run the code and compare both ternary operators—the original and the tuple syntax hack.

In fact, the order of the

Code:

<OnFalse>

and

Code:

<OnTrue>

operands is just flipped when compared to the basic ternary operator. First, you have the branch that’s returned if the condition does NOT hold. Second, you run the branch that’s returned if the condition holds.

Code:

age = 17 print(('wtf', 'What?')[age<20]) 'What?'

The condition

Code:

age<20

holds so the return value passed into the

Code:

print()

function is the

Code:

<OnTrue>

branch

Code:

'What?'

. Don’t worry if this confuses you—you’re not alone. Let’s clarify why this tuple syntax works the way it does!

First, you create a tuple

Code:

('wtf', 'What?')

. To access the first tuple value

Code:

'wtf'

, you’d use the standard indexing syntax

Code:

('wtf', 'What?')[0]

. To access the second tuple value

Code:

'What?'

, you’d use the standard indexing syntax

Code:

('wtf', 'What?')[1]

.

Second, you create a condition

Code:

age<20

. You use this condition as the indexing value. You end up with either

Code:

('wtf', 'What?')[False]

or

Code:

('wtf', 'What?')[True]

. As you may know, the Booleans

Code:

False

and

Code:

True

are represented through integers and

Code:

1

in Python. Thus, you get

Code:

('wtf', 'What?')[0]

and

Code:

('wtf', 'What?')[1]

, respectively.

In other words: if your condition evaluates to

Code:

False

, you access the first tuple value. If your condition evaluates to

Code:

True

, you access the second tuple value.

Where to Go From Here?

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