f-Strings

f-Strings#

Variables and strings can be combined, using f-strings. f-strings contain placeholders with variable names and format characters.

What are f-strings?#

f-strings are a powerful and convenient feature in Python that enhance the readability and maintainability of your code. They are the recommended method for string formatting in modern Python.

  • Introduced in Python 3.6, f-strings allow you to easily format strings by including variables and expressions directly within the string using curly braces {}.

  • They provide a concise and readable way to embed expressions within string literals.

Python f-strings (formatted string literals) provide a simple and concise way to embed expressions inside string literals.

Key advantages:

  • Readability: f-strings are more readable than older string formatting methods like % formatting or str.format().

  • Conciseness: They offer a more concise and elegant syntax.

  • Flexibility: You can use arbitrary expressions within the curly braces, including:

    • Variables

    • Function calls

    • Arithmetic operations

    • Conditional expressions

Syntax:#

To use an f-string, prefix the string with the letter f or F and enclose the expressions or variables you want to include within curly braces {}.

f"string with {expression}"

Details for using f-strings can be found in PEP 701 – Syntactic formalization of f-strings

Examples#

Basic Usage#

name = "Alice"
age = 30

# Using f-strings to format the string
greeting = f"My name is {name} and I am {age} years old."

print(greeting)

Output:

My name is Alice and I am 30 years old.

a=1
b=" a text string"
print(f'See how this works {a} and {b}')

See how this works 1 and  a text string

name = 'Roger'
number = 42
pi = 3.14159

    print(f'Hello {name}')

Hello Roger

    print(f'Result: {number:6d}')

Result:     42

    print(f'{number:06d}')

000042

    print(f'{name:>20} {name:20}')

               Roger Roger

Embedding Expressions#

You can embed any valid Python expression inside the curly braces.

x = 5
y = 10

# f-string with expressions
result = f"{x} + {y} = {x + y}"

print(result)

Output:

5 + 10 = 15

Formatting Numbers#

You can format numbers inside f-strings by adding formatting options after a colon : inside the curly braces.

pi = 3.14159

# Limiting float to 2 decimal places
formatted_pi = f"Value of pi: {pi:.2f}"

print(formatted_pi)

Output:

Value of pi: 3.14

Using f-strings with Dictionaries or Lists#

You can also access elements from dictionaries and lists inside f-strings.

person = {"name": "Alice", "age": 30}

# Accessing dictionary values in f-string
info = f"{person['name']} is {person['age']} years old."

print(info)

Output:

Alice is 30 years old.

name = "Alice"
age = 30

greeting = f"Hello, my name is {name} and I am {age} years old." 
print(greeting)  # Output: Hello, my name is Alice and I am 30 years old.

Complex expressions#

import math

radius = 5
area = math.pi * radius**2

print(f"The area of the circle is: {area:.2f}")  # Output: The area of the circle is: 78.54

Remark#

The older method .format() (prior to Python 3.6) is sometimes used for string formatting:

    a= 23.3
    b= 1.3
    print('{:6.3f}/{:6.3f}'.format(a, b))

23.300/ 1.300