Conditions — PythonLessonLab

THE IDEA

Understand the concept

A condition is an expression that Python evaluates as true or false. An if block runs only when its condition is true. Use elif for another test and else for the remaining case.

A colon ends each branch header, and indentation marks the statements inside that branch. Use == to compare values; = assigns a value to a name.

if, elif, and else
Boolean comparisons
Indented blocks

WORKED EXAMPLES

See it step by step

Read the code, predict the output, then compare it with the result.

01. Choose one branch

PYTHON

temperature = 30
if temperature >= 30:
    print("Hot")
else:
    print("Mild")

EXPECTED OUTPUT

Hot

The condition is true, so Python runs the indented first branch and skips else.

02. Use elif

PYTHON

points = 75
if points >= 90:
    print("Excellent")
elif points >= 60:
    print("Passed")
else:
    print("Try again")

EXPECTED OUTPUT

Passed

Python checks the conditions in order. Only the first matching branch runs.

HANDS-ON

Try it in Python

Edit the example and run it. Python starts in your browser the first time you click Run.

Python console

Ready to run

score = 78
if score >= 90:
    print("Excellent")
elif score >= 60:
    print("Passed")
else:
    print("Try again")

Need input()? Add one value per line

Input lines

Ctrl / ⌘ + Enter to run

OUTPUT

Your output appears here.

Your turnAdd a score == 100 branch before score >= 90 so an exact 100 prints 'Perfect'. Set score to 100 and run the program to test it.

Need a hint?

Place if score == 100 first. Change the old if score >= 90 to elif score >= 90, keep the remaining elif and else, then test with score = 100.

Complete the task and select Check task to verify your code.

KNOWLEDGE CHECK

Quick quiz

Three questions. You can change your answers and try again.

DEBUG BETTER

Typical mistakes

Everyone meets these errors. See what causes them and how to fix them.

Missing colon

COMMON MISTAKE

score = 75
if score >= 60
    print("Passed")

FIX

score = 75
if score >= 60:
    print("Passed")

What happens: SyntaxError on the if line.
End the if header with a colon.

Missing indentation