Functions in Python: How to Create and Use Them

December 7, 2023

Functions are an essential part of any programming language, and Python is no exception. In fact, functions are what make it possible for us to write complex and reusable code. In this lesson, we will learn how to create and use functions in Python, including passing arguments, returning values, and using built-in functions.

What is a Function?

A function is a block of code that performs a specific task. It takes in input, processes it, and produces an output. Functions allow us to break down our code into smaller and more manageable pieces, making it easier to read, debug, and maintain.

Creating Functions in Python

To create a function in Python, we use the def keyword followed by the name of the function and parentheses. We then add a colon at the end of the function name to indicate the start of the function’s code block. Let’s take a look at an example:

def greet():
    print("Hello, welcome to my blog!")

In the above code, we have defined a function called greet that prints out a greeting message. However, this function will not be executed until we call it.

Calling Functions in Python

To call a function in Python, we simply write the function name followed by parentheses. Let’s call our greet function from earlier:

greet()

This will print out the greeting message, “Hello, welcome to my blog!” on the screen. We can also call a function multiple times, allowing us to reuse the same code without having to write it again.

Passing Arguments to Functions

Functions can also take in input values, known as arguments, which can be used within the function’s code block. We specify the arguments inside the parentheses when defining the function. Let’s modify our greet function to take in a name as an argument:

def greet(name):
    print("Hello " + name + ", welcome to my blog!")

Now, when we call the greet function, we need to provide a name as an argument:

greet("John")

This will print out the message, “Hello John, welcome to my blog!” on the screen. We can also provide multiple arguments, separated by commas, if the function requires it.

Returning Values from Functions

Functions can also return values, which can be used in other parts of our code. To do this, we use the return keyword followed by the value we want to return. Let’s create a function that calculates the area of a rectangle:

def calculate_area(length, width):
    area = length * width
    return area

In the above code, we have defined a function called calculate_area that takes in two arguments, length and width, and calculates the area by multiplying them. Then, we use the return keyword to return the calculated area.

To use this function, we can assign the returned value to a variable and use it in our code:

rectangle_area = calculate_area(5, 10)
print(rectangle_area) # Output: 50

Built-in Functions in Python

Python also comes with a variety of built-in functions that we can use in our code without having to define them ourselves. These functions are already available to us and can be used for common tasks. Some examples of built-in functions in Python include print(), len(), and input().

Let’s take a look at an example of using the len() function, which returns the length of a string:

name = "John"
length = len(name)
print(length) # Output: 4

In the above code, we have used the len() function to get the length of the string “John” and assigned it to the variable length. We then print out the value of length, which is 4.

Conclusion

In this lesson, we have learned how to create and use functions in Python, including passing arguments, returning values, and using built-in functions. Functions are an essential part of any programming language and allow us to write efficient and reusable code. With practice, you will become comfortable with using functions and be able to incorporate them into your own projects.

Thank you for reading, and I hope you found this lesson helpful. Stay tuned for more posts on coding languages from scratch!