A function is a reusable block of code that performs a particular task. We write the code once inside a function and can call it whenever we need it.

 let's understand Python functions in a simple way, including args , **args ,**kwargs , default parameters, scope, closures, and lambda function.

What is a Function in Python?

A function is created using the def keyword.

def greet():
    print("Hello Sathwik!")

greet()

Output

Hello Sathwik!

Here, greet() is the function. When we call greet(), Python executes the code inside it.

Function with Parameters

Sometimes we want to send some information to a function. We can do this using parameters.

def greet(name):
    print("Hello", name)

greet("Sathwik")

Output

Hello Sathwik

Here, name is a parameter, and “Sathwik” is the value passed to that parameter.

Function with Return Value

A function can also return a result using the return keyword.

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

result = add(10, 20)

print(result)

Output

30

The return statement sends the result back to the place where the function was called.

Default Parameters

A default parameter is a parameter that already has a value.

def greet(name="Sathwik"):
    print("Hello", name)

greet()

Output

Hello Sathwik

If we provide another value, the default value is replaced.

def greet(name="Sathwik"):
    print("Hello", name)

greet("Rahul")

Output

Hello Rahul

Default parameters are useful when we want a function to work even if the user does not provide a particular value.

What is agrs  in Python?

 args means argument , the value passed to that parameter

def greet(name):
    print("Hello", name)

greet("Sathwik")

Output

Hello Sathwik

Here, name is a parameter, and “Sathwik” is  argument , the value passed to that parameter 

What is *agrs  in Python?

Sometimes we don't know how many arguments will be passed to a function.

This is where *args is useful.

*args allows a function to accept multiple positional arguments.

def add_numbers(*args):
    total = 0

    for number in args:
        total += number

    return total

print(add_numbers(10, 20))
print(add_numbers(10, 20, 30, 40))

Output

30
100

*args → multiple positional arguments

What is **kwargs  in Python?

**kwargs is used when we want to pass multiple keyword arguments to a function.

Keyword arguments are passed using a parameter name and value.

def student_details(**kwargs):
    for key, value in kwargs.items():
        print(key, ":", value)

student_details(
    name="Sathwik",
    age=21,
    course="Python"
)

Output

name : Sathwik
age : 21
course : Python

Inside the function, kwargs behaves like a dictionary.

**kwargs → multiple keyword arguments

Scope in Python

Scope means the area where a variable can be accessed.

There are mainly two important scopes when learning functions:

1. Local scope
2. Global scope

Local Scope

A variable created inside a function is called a local variable.

def student():
    name = "Sathwik"
    print(name)

student()

Here, name is available inside the function.

We cannot normally access it outside the function.

def student():
    name = "Sathwik"

student()

# print(name)  # This will cause an error

Global Scope

A variable created outside a function has global scope.

name = "Sathwik"

def greet():
    print(name)

greet()

Output

Sathwik

The function can access the global variable because it is defined outside the function.

Closures in Python

A closure happens when an inner function remembers and uses a variable from its outer function even after the outer function has finished executing.

def welcome(name):

    def message():
        print("Welcome", name)

    return message

greet = welcome("Sathwik")

greet()

Output

Welcome Sathwik

Here, message() is an inner function.

It uses the name variable from the outer function welcome().

Even after welcome() has finished, the inner function remembers the value “Sathwik”.

This is called a closure.

Closures are useful when we want a function to remember some information.

Lambda Functions

A lambda function is a small anonymous function.

Instead of using def, we can create a simple function using the lambda keyword.

For example:

square = lambda x: x * x

print(square(5))

Output

25

The same thing using a normal function would be:

def square(x):
    return x * x

print(square(5))

Lambda functions are generally useful when we need a small function for a short operation.