If-Then-Else in One Line Python – Finxter

Fast reply: How you can put a easy if-then-else assertion in a single line of Python code?

To place an if-then-else assertion in a single line, use Python’s ternary operator x if c else y. This returns the results of expression x if the Boolean situation c evaluates to True. In any other case, the ternary operator returns the choice expression y.

When you learn by the article to spice up your one-liner energy, you possibly can hearken to my detailed video clarification:

Right here’s one other minimal instance the place you come 21 if the situation 3>2 evaluates to True, in any other case, you come 42:

var = 21 if 3<2 else 42
# var == 42

The output 42 is saved within the variable var.

Introduction and Overview

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So the pure query arises: are you able to write conditional if-then-else statements in a single line of code?

This text explores this mission-critical query in all element.

Are you able to write the if-then-else assertion in a single line of code?

Sure, you possibly can write most if statements in a single line of Python utilizing any of the next strategies:

1. Write the if assertion with out else department as a Python one-liner: if 42 in vary(100): print("42").
2. If you wish to set a variable, use the ternary operator: x = "Alice" if "Jon" in "My identify is Jonas" else "Bob".
3. If you wish to conditionally execute a operate, nonetheless use the ternary operator: print("42") if 42 in vary(100) else print("21").

Within the earlier paragraph, you’ve unwillingly realized in regards to the ternary operator in Python.

The ternary operator is one thing you’ll see in most superior code bases so be certain that to grasp it completely by studying the next part of this text.

I drew this image to point out visually how the ternary operator works:

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

Associated articles: Python One Line Ternary

How you can Write the If-Then-Else Assertion as a Python One-Liner?

Let’s take a look in any respect the methods how one can write the if-then-else assertion in a single line.

The trivial reply is to only write it in a single line—however provided that you don’t have an else department:

Case 1: You Don’t Have an Else Department

Take into account the next code snippet the place you examine for the quantity 42 whether or not it falls in a variety of numbers:

>>> if 42 in vary(100):
>>>     print("42")
42

This code snippet will certainly print the output as a result of the integer 42 falls into the vary of numbers from 0 to 99.

However how can we write this if assertion in a single line of code?

Simply use a single line like this:

>>> if 42 in vary(100): print("42")
42

The 2 statements are similar so that is the best way to do it—for those who can write the conditional physique in a single line of code.

Nevertheless, for those who attempt to change into too fancy and you utilize a nested if physique, it received’t work:

>>> if 42 in vary(100): print("42") else print("21")
# "Error: invalid syntax"

Python can not deal with this anymore: the interpreter throws an “invalid syntax” error as a result of the assertion grew to become ambiguous.

However don’t fear, there’s a workaround: the ternary operator.

Case 2: You Have an Else Department And You Need to Conditionally Assign a Worth

In case you may have an else department and also you need to conditionally assign a price to a variable, the ternary operator is your buddy.

Say, you need to write the next if-then-else assertion in a single line of code:

>>> if "Jon" in "My identify is Jonas":
>>>     x = "Alice"
>>> else:
>>>     x = "Bob"
>>> print(x)
Alice

Because the string "Jon" seems within the string "My identify is Jonas", the variable x will take worth "Alice".

Can we write it in a single line? Certain—through the use of the ternary operator.

x = "Alice" if "Jon" in "My identify is Jonas" else "Bob"

The ternary operator could be very intuitive. Simply learn it from left to proper and also you’ll perceive its that means.

We assign the worth "Alice" to the variable x in case the next situation holds: "Jon" in "My identify is Jonas". In any other case, 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 extra intuitively as:

<OnTrue> if <Situation> else <OnFalse>

Case 3: What If You Don’t Need to Assign Any Worth However You Have an Else Department?

Effectively, there’s a fast and soiled hack: simply ignore the return worth of the ternary operator.

Say, we need to compress the next if-then-else assertion in a single line of code:

if 42 in vary(100):
    print("42")
else:
    print("21")

The issue is that we don’t have a return worth. So can we nonetheless use the ternary operator?

Because it seems, we will. Let’s write this if-then-else assertion in a single line:

>>> print("42") if 42 in vary(100) else print("21")
42

We use the ternary operator. The return worth of the print() operate is solely None. However we don’t actually care in regards to the return worth, so we don’t retailer it in any variable.

We solely care about executing the print operate in case the if situation is met.

How you can Write an If-Elif-Else Assertion in a Single Line of Python?

Within the earlier paragraphs, you’ve realized that we will write the if-else assertion in a single line of code.

However are you able to one-linerize an elif expression with a number of circumstances?

In fact, you possibly can!

(Heuristic: Should you’re unsure about whether or not you are able to do XYZ in a single line of Python, simply assume which you can. See right here.)

Say, you need to write the next if-then-else situation in a single line of code:

>>> x = 42
>>> if x > 42:
>>>     print("no")
>>> elif x == 42:
>>>     print("sure")
>>> else:
>>>     print("possibly")
sure

The elif department wins! We print the output "sure" to the shell.

However the right way to do it in a single line of code? Simply use the ternary operator with an elif assertion received’t work (it’ll throw a syntax error).

The reply is easy: nest two ternary operators like so:

>>> print("no") if x > 42 else print("sure") if x == 42 else print("possibly")
sure

If the worth x is bigger than 42, we print "no" to the shell.

In any other case, we execute the rest of the code (which is a ternary operator by itself). If the worth x is the same as 42, we print "sure", in any other case "possibly".

So by nesting a number of ternary operators, we will significantly enhance our Python one-liner energy!

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The e book is launched in 2020 with the world-class programming e book writer NoStarch Press (San Francisco).

Associated Questions

Let’s rapidly deal with a bunch of associated questions:

How you can Write If With out Else in One Line?

We’ve already seen an instance above: we merely write the if assertion in a single line with out utilizing the ternary operator: if 42 in vary(100): print("42").

Python is completely in a position to perceive a easy if assertion with out an else department in a single line of code.

How you can Write Elif in One Line?

We can not straight write the elif department in a single line of Python code. However we will nest two ternary operators as an alternative:

>>> 100 if x > 42 else 42 if x == 42 else 0
42

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

The ternary operator at all times returns the results of the conditional analysis. Once more, the code snippet 100 if x>42 else 42 returns the integer worth 42.

Should you solely execute capabilities throughout the ternary operator, it’ll return the None worth.

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Whereas working as a researcher in distributed methods, Dr. Christian Mayer discovered his love for instructing laptop science college students.

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