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Function in Python

 

Introduction

In this blog, we will learn about functions in Python. Functions are an integral part of any programming language and are used to structure and organize code. Functions are a way to break down a large and complex program into smaller, manageable and reusable blocks of code. In Python, functions are created using the "def" keyword and can be called using the function name followed by parenthesis. Functions are also referred to as "procedures" or "subroutines".

In this blog, we will cover the following topics:

  1. What are functions in Python?
  2. How to define a function in Python?
  3. Function arguments in Python
  4. Returning values from a function in Python
  5. Scope of variables in a function
  6. Recursion in Python
  7. Anonymous (Lambda) functions in Python
  8. Built-in functions in Python

Let's get started!

  1. What are functions in Python?

A function is a block of code that is executed only when it is called. Functions can take arguments (inputs) and return values (outputs). Functions are used to encapsulate a piece of code that performs a specific task, making it easier to maintain and reuse the code. By breaking down the code into smaller chunks, we can make our code more readable, maintainable, and reusable.

  1. How to define a function in Python?

Functions are defined in Python using the "def" keyword, followed by the function name, arguments (if any), and a colon. The body of the function is indented and contains the code that is to be executed when the function is called.

Here is a simple example to illustrate how to define a function in Python:


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

In the above example, we have defined a function called "greet" which prints "Hello, World!" when it is called.

  1. Function arguments in Python

Functions can accept arguments which can be used to pass data to the function. Arguments are specified in the function definition, within the parenthesis. In Python, functions can accept both required and optional arguments.

Required arguments are positional and must be passed in the same order as they are defined in the function. If a required argument is not passed, a TypeError is raised.

Here is an example of a function with required arguments:


def greet(name): 
    print("Hello, " + name + "!") 
greet("John")

Optional arguments are those that can be omitted when the function is called. These arguments have a default value specified in the function definition. If an optional argument is not passed, its default value is used.

Here is an example of a function with optional arguments:

scss
def greet(name, message="How are you?"):
    print("Hello, " + name + ". " + message)

greet("John")
greet("Jane", "How do     you do?")
  1. Returning values from a function in Python
python
def square(x): return x * x result = square(5) print(result) ``



Functions can return values using the "return" statement. The return statement terminates the execution of the function and returns the value specified after the return keyword. If no value is specified, the function returns "None".

Here is an example of a function that returns a value:


In the above example, the function "square" takes an argument x and returns its square. The function is then called with an argument 5 and the returned value is assigned to a variable result. Finally, the value of result is printed.

  1. Scope of variables in a function

In Python, the scope of a variable refers to the portion of the program where the variable is accessible. The scope of a variable in a function is limited to the body of the function. This means that variables defined inside a function are not accessible outside the function. On the other hand, variables defined outside a function are accessible inside the function.

Here is an example to illustrate the scope of variables in a function:

scss
x = 10 
 def print_x():
print(x) 
print_x()
print(x)
 def modify_x(): 
     x = 20 
    print(x)
modify_x() 
print(x)

In the above example, x is first defined outside the function with a value of 10. The function print_x is then defined, which prints the value of x. When print_x is called, it prints the value of x which is 10. Then, x is defined again inside the function modify_x with a value of 20. When modify_x is called, it prints the value of x inside the function, which is 20. However, when we print the value of x outside the function, it is still 10, as the definition of x inside the function does not affect the value of x outside the function.

  1. Recursion in Python

Recursion is a technique in which a function calls itself. A recursive function must have a base case, which is a condition that stops the recursion. If the base case is not met, the function calls itself with a modified argument.

Recursion is used to solve problems that can be broken down into smaller subproblems. For example, the factorial of a number can be calculated using recursion. The factorial of a number n is defined as n! = n * (n-1) * (n-2) * ... * 1. The base case for the factorial function is n! = 1 for n = 0 or n = 1.

Here is an example of a recursive function to calculate the factorial of a number:

python
def factorial(n): 
    if n == 0 or n == 1: 
        return 1 
    else:
        return n * factorial(n-1) 
result = factorial(5) 
print(result)

In the above example, the function factorial calculates the factorial of a number n. If n is 0 or 1, the function returns 1, which is the base case. If n is not 0 or 1, the function returns n multiplied by the factorial of n-1. The function keeps calling itself with n-1 until n becomes 0 or 1, at which point the base case is reached and the function returns 1. The final result of the function is the product of all the intermediate results.

  1. Anonymous (Lambda) functions in Python

In Python, anonymous functions are created using the lambda keyword. Anonymous


functions are also known as lambda functions. These are small, one-line functions that do not have a name. They are mainly used as arguments to other functions, such as map and filter.

Here is an example of using a lambda function as an argument to the map function:


numbers = [1, 2, 3, 4, 5]

squared_numbers = list(map(lambda x: x**2, numbers)) 
print(squared_numbers)

In the above example, the map function takes two arguments: the first argument is a lambda function that takes x as an argument and returns x**2, and the second argument is a list of numbers. The map function applies the lambda function to each element of the list and returns a new list with the squared numbers. The result of the map function is then converted to a list and assigned to the variable squared_numbers.

  1. Modules in Python

In Python, a module is a file containing definitions and statements that can be imported into other programs. Modules help to organize and reuse code. They provide a way to encapsulate functions, classes, and variables into a single unit, making it easier to manage and maintain large programs.

To import a module, you use the import statement. For example, to import the math module, you would write the following code:


import math

print(math.pi) 
print(math.sqrt(16))

In the above example, the math module is imported, and the constant pi and the function sqrt are used to calculate the square root of 16.

You can also import specific definitions from a module using the from keyword. For example, to import the pi constant from the math module, you would write the following code:


from math import pi 
print(pi)

In the above example, only the pi constant is imported from the math module. This can make your code more readable and reduce the risk of naming conflicts.

  1. Packages in Python

In Python, a package is a collection of modules organized into a directory. Packages provide a way to organize and reuse code in a hierarchical manner. They make it easier to manage and maintain large programs by grouping related modules together.

To create a package, you need to create a directory and place modules inside it. The directory must contain a file named __init__.py, which can be an empty file or can contain initialization code for the package.

Here is an example of creating a package:

python
# create a directory named `mypackage`
# create a file named `__init__.py` in the directory
# create a module named `mymodule.py` in the directory

# in mymodule.py
def square(x):
    return x**2 
# in another program

import mypackage.mymodule 
 result = mypackage.mymodule.square(5)
print(result)

In the above example, a directory named mypackage is created, and a file named __init__.py and a module named mymodule.py are placed inside the directory. The mymodule.py file contains a function named square that calculates the square of a number. In another program, the `my moduleis imported from themypackagepackage and thesquarefunction is used to calculate the square of5.


By bilyat

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