Python f-string

A Python f-string (formatted string literal) allows you to insert variables or expressions directly into a string by placing them inside curly braces {}.

This method makes your code more readable and is often faster than other string formatting techniques.

name = "Jennifer"
age = 23

# Use f-string to embed the name and age variables in a string
message = f"My name is {name} and I am {age} years old."

print(message)

# Output: My name is Jennifer and I am 23 years old.

Syntax of Python f-string

The f-string starts with f or F followed by quotation marks. Place any variables or expressions you want to embed within curly braces {} inside the string.

For example,

f"string with {expression}"

Here,

• f or F: Prefix the string with f or F to designate it as an f-string.
• " ": Use either double or single quotes around the string.
• {expression}: Place any variable, calculation, or expression inside curly braces {} to embed it within the string.

Example: Python f-string

language = "Python"

# Use f-string to embed the language variable in a string
text = f"Learn {language} with 'ProgramizPRO'."

print(text)

Output

Learn Python with 'ProgramizPRO'.

In the above example,

• f"Learn {language} with 'ProgramizPRO'." is the f-string.
• {language} is a placeholder for the language variable.

Evaluate Expression Inside f-string

You can perform calculations directly within the f-string. For example,

num1 = 5
num2 = 4

# Evaluate the sum of num1 and num2 inside f-string
result = f"Sum of {num1} and {num2} is {num1 + num2}."

print(result)

Output

Sum of 5 and 4 is 9.

Here, {num1 + num2} is an expression evaluated inside the f-string.

Python f-string Placeholder

You can place various expressions inside the placeholder of an f-string. For example,

Calling Functions Inside Placeholders

You can call a function directly within an f-string placeholder, and the return value will be embedded in the string.

def greeting():
    return "Good morning"

# Call greeting() inside f-string
text = f"{greeting()}, everyone!"

print(text)

# Output: Good morning, everyone!

Here, the function greeting() returns "Good morning", which is then placed directly into the f-string using {greeting()}.

Using Conditional Expressions Inside Placeholders

You can use conditional (if-else) expressions within an f-string placeholder to dynamically adjust the output based on variable values.

age = 18

# Using a conditional expression inside the f-string
text = f"You are {'an adult' if age >= 18 else 'a minor'}."

print(text)

# Output: You are an adult.

In this example:

• { 'an adult' if age >= 18 else 'a minor' } evaluates the condition.
• If age is 18 or older, it outputs "an adult"; otherwise, it outputs "a minor".

Access Dictionary Values Inside Placeholder

You can also access dictionary values directly within f-strings by using the dictionary key inside the curly braces {}.

person = {"country": "USA", "employee_ID": 121}

# Accessing dictionary values inside the f-string
text = f"Country: {person['country']}, Employee ID: {person['employee_ID']}"

print(text)

# Output: Country: USA, Employee ID: 121

In the above example, we have accessed the values of the person dictionary inside the f-string.

Here,

• {person['country']} is a placeholder that accesses the value of the country key.
• {person['employee_ID']} is a placeholder that accesses the value of the employee_ID key.

Tips for Using f-Strings

# Double quotes outside, single quotes inside
text = f"Learn {language} with 'ProgramizPRO'." 

# Single quotes outside, double quotes inside
text = f'Learn {language} with "ProgramizPRO".'  

# Causes a syntax error due to matching quotes inside and outside
text = f'Learn {language} with 'ProgramizPRO'.'
text = f"Learn {language} with "ProgramizPRO"."