What is an f-string in Python?

Master the art of string formatting in Python with our comprehensive guide to f-strings. Learn how to create dynamic strings, format variables, and more. …

Updated June 5, 2023

Master the art of string formatting in Python with our comprehensive guide to f-strings. Learn how to create dynamic strings, format variables, and more.

Definition

In Python 3.6 and later versions, a new way to create strings called f-strings (formatted string literals) was introduced. The name “f-string” comes from the fact that they are prefixed with an f before the string.

An f-string is essentially a formatted string literal, which allows you to insert expressions into a string using a simple syntax. This makes it easy to create dynamic strings where you can put any Python expression inside the {} placeholders.

Step-by-Step Explanation

To understand how f-strings work, let’s break down an example:

name = "John"
age = 30
greeting = f"Hello, {name}! You are {age} years old."

Here’s what happens in this code snippet:

We assign the string "Hello, {}! You are {} years old." to a variable greeting.
We use an f-string by prefixing the string with an f. This allows us to use expressions inside the {} placeholders.
Inside the first {}, we put the expression name, which is assigned to "John".
Inside the second {}, we put the expression age, which is assigned to 30.

When you run this code, Python will replace the expressions inside the {} placeholders with their actual values and return a new string:

greeting = "Hello, John! You are 30 years old."

How F-Strings Relate to Strings in Python

Before f-strings were introduced, Python provided several ways to format strings, including:

Using the % operator (string formatting)
Using the str.format() method
Using the format() function

While these methods still work today, f-strings offer a simpler and more readable way to create dynamic strings.

Here’s an example of how you can achieve similar results using string formatting with the % operator:

name = "John"
age = 30
greeting = "Hello, %s! You are %d years old." % (name, age)

As you can see, using f-strings is much cleaner and easier to read.

Advanced Use Cases

F-strings are not limited to simple string formatting. You can use them with complex expressions and even function calls:

x = 10
y = 20
result = f"The result of {x} + {y} is {x + y}"

You can also use f-strings with conditional statements, like this:

name = "John"
if name == "John":
    greeting = f"Hello, {name}!"
else:
    greeting = f"{name}, welcome!"

Conclusion

In conclusion, f-strings are a powerful tool for creating dynamic strings in Python. They offer a simple and readable way to format variables and expressions into strings. Whether you’re working on a small script or a large project, f-strings can help you write more efficient and maintainable code.