How to Use Python If-Else Statements

Materials Required: Latest version of Python (Python 3), an integrated development environment (IDE) of your choice (or terminal), and a stable internet connection.

Prerequisites/helpful expertise: Basic knowledge of Python and programming concepts

Conditional statements allow us to control what a program does through logic. They enhance our programs by equipping them with decision-making capabilities. By the end of this tutorial, you will be able to use conditional statements like if-else to establish rules for your program to follow.

Glossary

What is a Python if statement?

If is a conditional statement used for decision-making operations. In other words, it enables the programmer to run a specific code only when a certain condition is met. The body of a Python if statement begins with indentation. The first unindented line marks the end. Remember that non-zero values are interpreted by Python as True while None and 0 are False.

Example of an if statement in Python:

How if statements work in Python

First, the program evaluates your test expression. If it is true, the statement (or statements) will be executed. If it is false, the statement(s) will not be executed. The following flow chart demonstrates how an if statement works in Python:

Try it yourself

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x = 73
y = 55

#Write an if statement that prints "x is greater than y" when true

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x = 73
y = 55

if x > y:
  print("x is greater than y")

What is a Python if-else statement?

An if-else statement adds onto the function of an if statement. Instead of simply refraining from executing statement(s) when the test expression is false, it provides alternative instructions for the program to follow. You’ll use indentation to separate the if and else blocks of code.

Example of an if-else statement in Python:

How if-else statements work

The program evaluates your test expression. If it is true, the statement (or statements) will be executed. If it is false, the program will follow the alternative instructions provided. The following flow chart demonstrates how an if-else statement works in Python:

How to write an if-else statement in Python

Here’s a breakdown of the syntax of an if-else statement:

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if #expression:
    #statement
else:
    #statement

Try it yourself

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fruits = ["apple","orange","banana","grape","pear"]
item = "cucumber"

#Write an if-else statement that prints "[item] is a fruit" or "[item] is not a fruit" 
#depending on whether it's in the list of fruits

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fruits = ["apple","orange","banana","grape","pear"]
item = "cucumber"

if item in fruits:
  print(item + " is a fruit")
else:
  print(item + " is not a fruit")

How to use an if-else statement in Python

If you need a program to execute certain functions under specific conditions, you should use an if-else statement. Conditional statements like if-else are also known as conditional flow statements. This name comes from the ability to control the flow of your code on a situational basis. It can be helpful to think of conditional statements as a set of rules for Python to follow.

What is elif in Python?

Elif is the shortened version of else if. It enables you to perform a series of checks to evaluate the conditions of multiple expressions. For example, suppose the first statement is false, but you want to check for another condition before executing the else block. In that case, you can use elif to look for the other specified condition before Python decides which action to take. You can have any number of elif statements following an if statement.

Example of an if-elif-else statement:

Here, each number from -2 to 1 gets passed through the if-elif-else statement. Once a condition is true, the interpreter executes that block of code.

How if-elif-else else works in Python

The interpreter will evaluate multiple expressions one at a time, starting with the if statement. Once an expression is evaluated as True, that block of code will execute. If no expression is True, the else statement will execute. The following flow chart demonstrates how an if-elif-else statement works in Python:

What is a nested if-else statement?

In programming, “nesting” is a term that describes placing one programming construct inside another. For example, suppose you have more than two options to handle in your code. In that case, you can use a nested if-else statement to check conditions in consecutive order. Once a condition succeeds, it will move on to the next block. In the event that none of the conditions are true, the else clause will take effect.

Example of a nested if-else statement:

The interpreter starts by evaluating the first number in the range, in this case, -2. Since the first if statement is True for -2, the interpreter will then evaluate the if statement nested within the first if statement. If True again, it will execute that block of code. If False, it will execute the nested else statement. The process repeats for each number in the range.

How a nested if-else statement works in Python

Nested statements allow programmers to use minimal code by organizing information into layers where one object contains other similar objects.

Key takeaways

• if, else, and elif are conditional statements used for decision-making operations.
• You can use an if statement when you don’t need anything to be done if the condition is false.
• You can use an else statement to provide further instructions for when a condition is false.
• Use elif when you need to check for multiple conditions.
• Nested if-else statements can be used when you have more than two options in your code.

Resources

Click here to find a downloadable cheat sheet for the tutorial above. You can also get involved with the Python community to stay current on tips and recent releases by subscribing to the free Python email newsletter or connecting with peers by joining the Python programming Slack channel.

• Python traceback tutorial
• Python exception handling cheat sheet
• Being a Python Developer: What They Can Do, Earn, and More
• Python control flow tools documentation

Continue building your Python expertise with Coursera.

Decision-making operations are essential programming concepts. You can practice using conditional statements by developing your own interactive game through a Guided Project like Python Basics: Create a Number Game from Scratch. Or, take the next step in mastering the Python language and earn a certificate from the University of Michigan in Python 3 Programming.