String formatting using f-strings in Python

Introduction

F-strings help you put values inside text easily and clearly. They make your messages or results look nice and readable.

When you want to show a message with numbers or names mixed in.

When you need to create a sentence that includes changing information.

When you want to print results from calculations inside a sentence.

When you want to build a file name or path using variables.

When you want to format dates or prices neatly in text.

Syntax

Python

f"text {variable} more text {expression}"

Start the string with the letter f before the quotes.

Put variables or expressions inside curly braces {} to include their values.

Examples

Insert a variable name inside the text.

Python

name = "Anna"
print(f"Hello, {name}!")

Show a number variable inside a sentence.

Python

age = 25
print(f"You are {age} years old.")

Calculate inside the braces and show the result.

Python

x = 5
y = 3
print(f"Sum is {x + y}.")

Format a number to 2 decimal places.

Python

price = 9.99
print(f"Price: ${price:.2f}")

Sample Program

This program shows how to use f-strings to print variables and expressions in sentences.

Python

name = "Sam"
age = 30
height = 1.75

print(f"Name: {name}")
print(f"Age: {age} years")
print(f"Height: {height} meters")
print(f"Next year, {name} will be {age + 1} years old.")

Important Notes

You can put any expression inside the braces, like math or function calls.

F-strings work only in Python 3.6 and later versions.

Use :.2f inside braces to format floats with 2 decimals.

Summary

F-strings make it easy to mix text and values in one string.

Use curly braces {} to insert variables or expressions.

They help create clear and readable output messages.

Practice

1. What is the main purpose of using f-strings in Python?

easy

A. To easily insert variables or expressions inside strings

B. To create lists from strings

C. To convert strings to uppercase

D. To repeat strings multiple times

Solution

1. Step 1: Understand f-string usage

   F-strings allow embedding variables or expressions inside strings using curly braces {}.

2. Step 2: Compare options

   Only To easily insert variables or expressions inside strings describes this purpose correctly; others describe unrelated string operations.

3. Final Answer:

   To easily insert variables or expressions inside strings -> Option A

4. Quick Check:

   f-strings = insert variables in strings [OK]

Hint: Remember: f-strings embed variables with curly braces {} [OK]

Common Mistakes:

• Confusing f-strings with string methods like upper()
• Thinking f-strings create lists
• Assuming f-strings repeat strings

2. Which of the following is the correct syntax to use an f-string to insert variable name into a string?

easy

A. "Hello, $name!"

B. f"Hello, {name}!"

C. f'Hello, $name!'

D. "Hello, {name}!"

Solution

1. Step 1: Identify f-string syntax

   An f-string starts with the letter f before the quotes and uses curly braces {} to insert variables.

2. Step 2: Check each option

   f"Hello, {name}!" correctly uses f"Hello, {name}!". Options A and B lack the f prefix, and C uses incorrect syntax with $name.

3. Final Answer:

   f"Hello, {name}!" -> Option B

4. Quick Check:

   f-string = f"text {var}" [OK]

Hint: f-string must start with f and use {variable} inside quotes [OK]

Common Mistakes:

• Omitting the f before the string
• Using $ instead of curly braces
• Using single quotes without f prefix

3. What will be the output of this code?

name = "Alice"
age = 30
print(f"{name} is {age} years old.")

medium

A. name is age years old.

B. {name} is {age} years old.

C. SyntaxError

D. Alice is 30 years old.

Solution

1. Step 1: Evaluate variables inside f-string

   The variables name and age are replaced by their values "Alice" and 30 inside the string.

2. Step 2: Understand print output

   The print statement outputs the string with variables replaced: "Alice is 30 years old.".

3. Final Answer:

   Alice is 30 years old. -> Option D

4. Quick Check:

   f-string replaces {name} and {age} with values [OK]

Hint: f-string prints variable values, not variable names [OK]

Common Mistakes:

• Expecting curly braces to print literally
• Confusing variable names with values
• Thinking f-string causes syntax error here

4. Find the error in this code snippet:

age = 25
print(f"Age is {age")

medium

A. Missing closing brace '}' in f-string

B. Missing f before the string

C. Variable age is not defined

D. Incorrect use of quotes

Solution

1. Step 1: Check f-string braces

   The f-string has an opening brace { but no matching closing brace }, causing a syntax error.

2. Step 2: Verify other parts

   The f prefix is present, variable age is defined, and quotes are correct.

3. Final Answer:

   Missing closing brace '}' in f-string -> Option A

4. Quick Check:

   Every { must have a matching } in f-string [OK]

Hint: Count braces in f-string; each { needs a } [OK]

Common Mistakes:

• Forgetting to close curly braces
• Thinking missing f causes this error
• Assuming variable is undefined

5. You want to print the price of an item with 2 decimal places using f-strings. Which code correctly formats the price variable?

price = 9.8765
# Choose the correct print statement

hard

A. print(f"Price: ${price:2f}")

B. print(f"Price: ${price:.2}")

C. print(f"Price: ${price:.2f}")

D. print(f"Price: ${price:.2d}")

Solution

1. Step 1: Understand format specifier for decimals

   To format a float with 2 decimal places, use :.2f inside the curly braces.

2. Step 2: Check each option

   print(f"Price: ${price:.2f}") uses {price:.2f} correctly. print(f"Price: ${price:2f}") misses the dot, print(f"Price: ${price:.2}") misses the type specifier, and print(f"Price: ${price:.2d}") uses invalid d for decimals.

3. Final Answer:

   print(f"Price: ${price:.2f}") -> Option C

4. Quick Check:

   Use :.2f to format float with 2 decimals [OK]

Hint: Use :.2f inside {} to show 2 decimal places [OK]

Common Mistakes:

• Omitting the dot before precision
• Using integer format 'd' for floats
• Leaving out the type specifier