Functions

Functions in Python are blocks of reusable code that perform a specific task. They help in organizing code, making it more modular, and improving readability. Functions are especially useful when the same task needs to be performed multiple times. Here's a breakdown of key aspects of functions in Python:

Defining a Function

Functions in Python are defined using the def keyword.

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

Calling a Function

To execute a function, use its name followed by parentheses.

greet()  # Output: Hello, World!

Function Parameters

Functions can accept input in the form of parameters, which allow them to process dynamic data.

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

greet("Jasmeet")  # Output: Hello, Jasmeet!

Default Parameters You can define default values for parameters, making them optional when calling the function.

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

greet()         # Output: Hello, Guest!
greet("Chris")    # Output: Hello, Chris!

Return Statement

Functions can return a value using the return keyword.

def add(a, b):
    return a + b

result = add(5, 3)
print(result)  # Output: 8

Variable Scope

Variables defined inside a function have local scope and are not accessible outside the function.

y = 11     # This is a Global variable 
def func():
    x = 10  # Local variable
    print(y)   

func()      # Output : 11
# print(x)  # This will raise an error since x is not defined outside the function.

Lambda Functions

Lambda functions are anonymous, single-expression functions. They're defined using the lambda keyword.

add = lambda x, y: x + y
print(add(5, 3))  # Output: 8

Nested Functions

Functions can be defined inside other functions.

def outer_function():
    def inner_function():
        print("Inner function")
    inner_function()

outer_function()

Higher-Order Functions

Functions can accept other functions as arguments or return them.

def apply_function(func, value):
    return func(value)

result = apply_function(lambda x: x**2, 5)
print(result)  # Output: 25

Decorators

Decorators are special functions that modify the behavior of another function.

def decorator(func):
    def wrapper():
        print("Before the function call")
        func()
        print("After the function call")
    return wrapper

@decorator
def say_hello():
    print("Hello!")

say_hello()

Built-in Functions

Python provides several built-in functions, such as len(), max(), min(), print(), sum(), etc.

numbers = [1, 2, 3, 4, 5]
print(sum(numbers))  # Output: 15

Functions are a cornerstone of Python programming, allowing you to build efficient, maintainable, and scalable code.