String Formatting — PythonLessonLab

THE IDEA

Understand the concept

An f-string places a value inside a string when you write an f before the opening quote. Curly braces mark each expression to evaluate. This is useful for labels, messages, and summaries.

A format specifier inside the braces can control display. For example, :.2f shows a floating-point value with two digits after the decimal point.

Prefix a string with f
Use {expression} placeholders
Format decimals with :.2f

WORKED EXAMPLES

See it step by step

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

01. Insert two values

PYTHON

student = "Ava"
topic = "lists"
print(f"{student} is studying {topic}.")

EXPECTED OUTPUT

Ava is studying lists.

The f before the string tells Python to replace each {name} with its current value.

02. Format a decimal

PYTHON

score = 7.5
print(f"Score: {score:.2f}")
print(f"Next lesson: {2 + 1}")

EXPECTED OUTPUT

Score: 7.50
Next lesson: 3

The :.2f format displays two decimal places; an f-string can also evaluate an expression.

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

student = "Maya"
completed = 3
score = 8.75
print(f"{student} finished {completed} lessons.")
print(f"Quiz score: {score:.2f}")

Need input()? Add one value per line

Input lines

Ctrl / ⌘ + Enter to run

OUTPUT

Your output appears here.

Your turnCreate a variable called topic with the value "loops". Print "Maya is studying loops." using an f-string.

Need a hint?

Set topic = 'loops'. In an f-string, put {student} and {topic} inside braces, and include the exact punctuation at the end.

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 f prefix

COMMON MISTAKE

name = "Maya"
print("Hi, {name}")

FIX

name = "Maya"
print(f"Hi, {name}")

What happens: The literal text Hi, {name} is displayed.
Add f before the opening quote to evaluate placeholders.

Unknown placeholder