Python Define Function | Docs With Examples

Functions in Python are reusable blocks of code that perform a specific task. They improve code readability, reusability, and organization.

Defining a Function with def

In Python, you define a function using the def keyword:

def greet(): print("Hello, World!")

Explanation:

• def is the keyword used to define a function.
• greet is the function name.
• The parentheses () can hold parameters (discussed next).
• The function body is indented and contains the logic to be executed.

Calling a Function

Once a function is defined, call it by using its name followed by parentheses:

greet()

Output:

Hello, World!

Function Parameters

You can pass values to a function using parameters:

def greet_user(name): print(f"Hello, {name}!") greet_user("Alice")

Output:

Hello, Alice!

Explanation: The function takes one parameter, name, and uses an f-string to personalize the greeting.

Default Parameters

You can provide default values for parameters:

def greet_user(name="Guest"): print(f"Hello, {name}!") greet_user()

Output:

Hello, Guest!

Returning Values

Functions can return values using return:

def add(a, b): return a + b result = add(3, 5) print(result)

Output:

8

Multiple Return Values

Functions can return multiple values as a tuple:

def get_coordinates(): return 10, 20 x, y = get_coordinates() print(x, y)

Output:

10 20

Keyword Arguments

You can specify arguments using keywords for clarity:

def introduce(name, age): print(f"My name is {name} and I am {age} years old.") introduce(age=30, name="Bob")

Output:

My name is Bob and I am 30 years old.

Variable-Length Arguments

*args (Multiple Positional Arguments)

Use *args to accept a variable number of arguments:

def sum_numbers(*args): return sum(args) print(sum_numbers(1, 2, 3, 4, 5))

Output:

15

**kwargs (Multiple Keyword Arguments)

Use **kwargs to accept multiple keyword arguments:

def display_info(**kwargs): for key, value in kwargs.items(): print(f"{key}: {value}") display_info(name="Alice", age=25, city="New York")

Output:

name: Alice age: 25 city: New York

Nested Functions

Functions can be defined inside other functions:

def outer_function(): def inner_function(): print("This is an inner function.") inner_function() outer_function()

Output:

This is an inner function.

Lambda Functions (Anonymous Functions)

A lambda function is a short function with no name:

square = lambda x: x ** 2 print(square(4))

Output:

16

Key Takeaways

• Use def to define functions for reusable logic in your Python projects.
• Functions can accept parameters, return values, and handle flexible arguments.
• *args allows multiple positional arguments.
• **kwargs allows multiple keyword arguments.
• Use lambda functions for short, anonymous operations.

Practice Exercise

Here's a simple challenge, open up your Python editor and try to write a function that takes two numbers and returns their product:

def multiply(a, b): return a * b print(multiply(6, 7))

Wrapping Up

Understanding how to define and use functions is crucial for writing efficient and organized Python code. Functions enhance modularity, making code easier to read and maintain. Happy coding!