Python Tutorial



Python Tutorial

F-string in Python


In Python, there are several ways to format strings. Properly formatted strings are essential for displaying data or messages in a readable and organized manner. F-strings have emerged as a modern and elegant solution for string formatting. Python's readability and ease of use have always been key attributes, and F-string in Python takes this to a new level. These Formatted String Literals, introduced in Python 3.6, simplify how developers create formatted strings, allowing for effortlessly embedding variables and expressions within text.

In this article, we will delve into F-strings' abilities, exploring their intuitive syntax, versatile capabilities, and the numerous advantages they offer over older string formatting methods. From basic usage to more advanced features, you'll learn how F-strings streamline the process of constructing clear and concise strings in Python.


F-string in Python, or Formatted String Literals, is a feature introduced in Python 3.6 to simplify and enhance how strings are formatted. They provide a concise, more readable way to embed expressions and variables within strings. F-strings are ideal for string interpolation and formatting.

Old String Formatting in Python

This method is also known as "print-style" formatting and has been available in Python for a long time. 

A) % - Formatting

How to use % - Formatting

The % operator, often referred to as the "modulo" or "interpolation" operator, is an older method for string formatting in Python. It involves using placeholders within a string, which are replaced with values when the string is generated. The placeholders are represented by %s, %d, %f, and other format codes.

Example 1:

Python code

name = "Alice"
age = 30
print("Name: %s, Age: %d" % (name, age))

Output 1:

Name: Alice, Age: 30

Example 2:

Python code

price = 19.99
quantity = 3
total = price * quantity
print("Price: $%.2f, Quantity: %d, Total: $%.2f" % (price, quantity, total))

Output 2:

Price: $19.99, Quantity: 3, Total: $59.97

Example 3:

Python code

city = "New York"
temperature = 70.5
print("City: %s, Temperature: %.1f°F" % (city, temperature))

Output 3:

City: New York, Temperature: 70.5°F

Example 4:

Python code

item = "Widget"
price = 24.95
print("Item: %s, Price: $%.2f" % (item, price))

Output 4:

Item: Widget, Price: $24.95

Why %-Formatting is not recommended?

%-formatting in Python is considered less recommended for several reasons:

  • Readability: The syntax used in %-formatting can make the code less readable and more complex, particularly when dealing with multiple placeholders or complex formatting requirements. This can lead to code that is harder to understand and maintain for new Python developers.

  • Limited Formatting Options: %-formatting provides a limited set of format codes (e.g., %s, %d, %f), which can be insufficient for more advanced formatting needs. It lacks the flexibility and expressiveness of other modern formatting methods.

  • Error-Prone: It's relatively easy to make mistakes when using %-formatting. Mismatched format codes and values or using the wrong format code can lead to runtime errors that can be challenging to debug and fix.

  • Obsolete for New Code: With the introduction of more modern and readable string formatting methods, such as str.format() and F-strings, %-formatting has become somewhat outdated for new code. These newer methods are considered more Pythonic and are preferred in modern Python development.

  • Not Recommended by PEP 8: PEP 8, the Python Enhancement Proposal for code style, recommends using str.format() or F-strings for string formatting. It explicitly discourages % formatting, signaling that it's not the recommended style in contemporary Python coding practices.

  • Python 2 vs. Python 3 Compatibility: %-formatting is associated with Python 2, which is no longer maintained since January 1, 2020. Using %-formatting can hinder the transition to Python 3, which is the actively maintained f-string Python version.

B) str.format() Method

How to Use str.format()

The str.format() method offers a more flexible and readable way to format strings. It involves using placeholders enclosed in curly braces {} within the string. These placeholders can be filled with values using the format() method, providing better formatting control.

Example 1:

Python code

name = "Bob"
age = 25
print("Name: {}, Age: {}".format(name, age))


Name: Bob, Age: 25

Example 2:

Python code

price = 29.99
quantity = 2
total = price * quantity
print("Price: ${:.2f}, Quantity: {}, Total: ${:.2f}".format(price, quantity, total))


Price: $29.99, Quantity: 2, Total: $59.98

Example 3:

Python code

country = "Canada"
population = 37664517
print("Country: {}, Population: {:,}".format(country, population))


Country: Canada, Population: 37,664,517

Example 4:

Python code

fruit = "Apple"
weight = 0.3
print("Fruit: {}, Weight: {:.1f} kg".format(fruit, weight))



Fruit: Apple, Weight: 0.3 kg

Why str.format() Method is not recommended?

While str.format() offers improved readability and more formatting options than % formatting, it is still not the most recommended method for a few reasons:

  • Complex Syntax: While str.format() is more readable than % formatting, it can become complex and verbose when you need to format multiple variables or apply complex formatting. Using placeholders and the .format() method can make the code less concise.

  • Less Concise: F string in Python offers a more concise and straightforward way to embed expressions and variables in strings. With F-strings, you can directly place variables and expressions within curly braces, eliminating the need for a separate .format() method.

  • Potential Clutter: In some cases, especially when dealing with many placeholders and formatting options, the code using str.format() can become cluttered and less elegant than F-strings.

  • Readability: While str.format() is more readable than % formatting, it may still be less intuitive for new Python developers when compared to the simplicity of F-strings.

  • Additional Function Call: Using str.format() involves a method call (i.e., .format()) in addition to defining placeholders, which can add some overhead to the code.

C) F-string Method

Using F-string in Python

F-strings, introduced in Python 3.6, offer a concise and intuitive way to format strings. You can embed expressions directly within strings, enclosed in curly braces {}. F-strings are widely favored for their readability and simplicity.

f-string Python Example 1:

Python code

name = "Carol"
age = 35
formatted_string = f"Name: {name}, Age: {age}"


Name: Carol, Age: 35

f-string Python format Example 2:

Python code

item = "Laptop"
price = 899.99
formatted_string = f"Item: {item}, Price: ${price:.2f}"


Item: Laptop, Price: $899.99

Example 3:

Python code

country = "France"
population = 67364357
formatted_string = f"Country: {country}, Population: {population:,}"


Country: France, Population: 67,364,357

Example 4:

Python code

fruit = "Banana"
weight = 0.25
formatted_string = f"Fruit: {fruit}, Weight: {weight:.2f} kg"


Fruit: Banana, Weight: 0.25 kg

D) F-string in Dictionary

Using F-strings to Format Dictionary Values

F-strings can also be used to format values from dictionaries. This is particularly useful when creating dynamic and informative output based on dictionary content.

f-string Python Example 1:

Python code

person = {'name': 'David,' 'age': 40}
formatted_string = f"Name: {person['name']}, Age: {person['age']}"


Name: David, Age: 40

f-string Python-format Example 2:

Python code

product = {'name': 'Smartphone,' 'price': 699.99}
formatted_string = f"Product: {product['name']}, Price: ${product['price']:.2f}"


Product: Smartphone, Price: $699.99

f-string format provide a seamless way to incorporate dictionary values into your strings, enhancing the readability and maintainability of your code.

E) Speed

Performance Comparison of Formatting Methods

String formatting methods can vary in performance. Let's compare the speed of % formatting, str.format(), and F-strings using the timeit module to measure execution times.

f-string Python Example 1:

Python code

import timeit

name = "Eve"
age = 29

# Measure the time for % formatting
%timeit "Name: %s, Age: %d" % (name, age)

# Measure the time for str.format()
%timeit "Name: {}, Age: {}".format(name, age)

# Measure the time for f-string in Python
%timeit f"Name: {name}, Age: {age}"

This code will provide the execution times for each formatting method, allowing you to compare their speed and choose the most efficient option for your specific use case.

F) Braces

Dealing with Curly Braces in Strings

When working with strings that need to display literal curly braces {}, you may encounter challenges, as these characters are used as placeholders in formatting methods. Using double curly braces allows you to include literal curly braces within your strings without causing conflicts with formatting placeholders. You can use double curly braces {{ and }} to display them as-is.

Example 1:

Python code

text = "This is {{curly braces}}"


This is {curly braces}

G) Backslashes

Handling Backslashes in Strings

Backslashes in strings can be tricky because they are typically used as escape characters.  By using double backslashes, you ensure that the backslashes are displayed as intended in the output. To display a literal backslash, you need to escape it by using an additional backslash \\.

Example 1:

Python code

path = "C:\\Windows\\System32"



H) Inline Comments

Adding Comments within Formatted Strings

In some cases, you may want to include comments within your formatted strings. These comments are for your reference and are ignored during execution. You can include comments by placing them within the formatted string, enclosed in curly braces {}.

f in Python Example 1:

Python code

name = "Frank"
age = 30
formatted_string = f"Name: {name}, Age: {age} {{comment: this is a comment}}"



Name: Frank, Age: 30 {comment: this is a comment}


In conclusion, string formatting is a crucial aspect of Python programming, as it enables you to present data and messages in a readable and organized manner. While older methods like % formatting and str.format() are still valid, modern approaches like f-string in Python offer better readability, simplicity, and versatility. The choice of formatting method should be based on your specific use case and coding style.


1. What's the fastest string formatting method in Python?

F-strings are generally the fastest, followed by str.format() and % formatting.

2. When should I use % formatting?

Use % formatting when working with legacy code or when it's a requirement in a project. However, consider more modern alternatives for new code.

3. Can I use F-strings for complex formatting?

Yes, F-strings support complex formatting and can handle most formatting needs efficiently.

4. How do I display literal curly braces or backslashes in strings?

Use double curly braces {{ and }} to display literal curly braces and escape backslashes with an additional backslash \\.

5. How do you use F-strings to format dictionary values? 

You can format dictionary values with F-strings using curly braces with variable or dictionary key references within the string. 

6. What is the performance difference between various string formatting methods in Python?

The speed of string formatting methods can vary. F-strings are generally the fastest, followed by str.format(), and %-formatting.

7. Can you add comments within formatted strings using F-strings? 

Yes, you can add comments within F-strings by placing comments within curly braces within the string. These comments are ignored during execution.

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