Defining a Function

Defining a Function in Python

Python is an open-source programming language that is commonly used for web development, scientific computing, data analysis, artificial intelligence, and more. One of the key features of Python is its ability to define and use functions.

What is a Function?

A function is a named block of code that performs a specific task. Functions help to organize code and make it more readable, maintainable, and reusable. Once a function is defined, it can be called multiple times from different parts of the program, avoiding code duplication.

Syntax for Defining a Function

In Python, functions are defined using the def keyword, followed by the function name, parentheses, and a colon. The function block is indented and contains the code that performs the task.

def function_name(arguments):
    function code

The function name should follow the same conventions as variable names and be descriptive of the task it performs. The function can take arguments, which are input values provided to the function when it is called.

Example of a Function

Let’s define a simple function that takes two numbers as arguments and returns their sum.

def add_numbers(num1, num2):
    return num1 + num2

In this example, the function name is add_numbers, and it takes two arguments. The code block adds the two numbers and returns the result using the return keyword.

Calling a Function

Once a function is defined, it can be called from other parts of the program using the function name and passing the required arguments.

result = add_numbers(3, 5)

In this example, we are calling the add_numbers function and passing it two arguments, 3 and 5. The result of the function is stored in the result variable.

Default Arguments

In Python, it is possible to define default arguments for a function. Default arguments are values that will be used automatically if no value is provided when the function is called.

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

In this example, the greet function takes two arguments: name and greeting. If no greeting is provided, the default value of “Hello” will be used.

Keyword Arguments

Keyword arguments in Python allow you to name the arguments when calling a function, so the order in which they are supplied does not matter.

def divide_numbers(num1, num2):
    return num1 / num2

result = divide_numbers(num2=2, num1=10)

In this example, we are invoking the divide_numbers function using keyword arguments. The order of the arguments doesn’t matter as long as they are named correctly.


Defining functions is an essential element of programming in Python. It helps to organize code, make it more readable and reusable, and avoid code duplication. This tutorial covered the syntax for defining a function, calling a function, default and keyword arguments.

With this knowledge, you can expand your programming skills and write more complex and efficient programs using functions.

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