Understanding Python Functions: A Practical Overview

As a programmer, you will often find yourself performing an action or task repeatedly. This can be tedious and time-consuming, especially when working with a large or complex code base. Automating them with functions is a more effective approach to performing such tasks. Functions allow you to write the code logic once and use it anywhere in your program.

What Is a Python Function?

In Python, a function is a block of code used to perform a specific task. You only need to write a function once, but you can use it multiple times in your code. A function can take in arguments as input and return output values. This simple program shows a function that calculates the sum of three numbers:

 

def calculate_sum(a, b, c):
    return a+b+c

print(calculate_sum(1,2,3)) 
print(calculate_sum(1000, 300,44)) 
print(calculate_sum(12, 4,78)) 
 

In the program above, the function returns the sum of three arguments. When the function is called multiple times, it returns a different output for each case. A useful application for this function will be a calculator app.

Defining a Function in Python

Python has many built-in functions available for developers to use. However, these built-in functions are not always enough to meet the demands of most projects. To meet custom demands, you have to define your custom functions. Defining custom functions is common practice in programming.

In Python, you can define a custom function by using the def keyword followed by the name of your function with parenthesis in front of it. Here is an example:

 def function_name()
 

You should take note of these rules when assigning a function name in Python:

• Function names should be in lowercase.
• Function names should be descriptive.
• Use underscores to separate words in a function name.

After defining the function, you must write the logic to perform your desired task. For example, this function calculates the area of a triangle:

 

def calculate_triangle_area(base, height):
    area = (base * height)/2
    return area

print(calculate_triangle_area(12, 3))
 

The function above defines two parameters: base and height, divides their product by two, and returns the result as the output. You can write whatever logic you want your function to perform.

Understanding Function Arguments

In previous examples, the functions have taken arguments to perform actions. The arguments in these examples are known as required or positional arguments. In Python, your arguments can be either of the following:

• Positional arguments
• Keyword arguments

Positional Arguments

Positional arguments need to be passed in the correct order of definition. For example, if you define a function with parameters a, b, and c, you must pass in values for these parameters accordingly when you call them. Let us examine a previous example:

 

def calculate_sum(a, b, c):
    return a+b+c

print(calculate_sum(1,2,3)) 
print(calculate_sum(1000, 300,44)) 
print(calculate_sum(12, 4,78)) 
 

In the above program, the calculate_sum() function takes three arguments whenever we call it. Each argument represents a corresponding parameter. In the first function call, numbers 1, 2, and 3 represent a, b, and c accordingly.

A parameter is declared in a function’s definition, while an argument is the value passed when you call the function This value is a representation of its corresponding parameter.

Positional arguments are compulsory. If you don’t add them, you will get a TypeError. The following example demonstrates this:

 def calculate_sum(a, b, c):
    return a+b+c

print(calculate_sum(1,2)) 
 

When you run the above program on your machine, you will get an error similar to the one in the image below:

Keyword Arguments

Keyword arguments do not necessarily need to be passed whenever you call a function. They are optional arguments and don’t need to follow a specific order. Python lets us use *args and **kwargs to specify keyword arguments.

Apart from using *args and **kwargs, it is also possible to specify default values for your arguments. Doing this will not get an error if you forget to add a value when calling the function. This example gives an illustration:

 def calculate_sum(a, b, c=3):
    return a+b+c

print(calculate_sum(1,2)) 
 

In the above program, when calculate_sum() is called, there is no argument for c; this will not affect the program because c already has a default value. You can specify default values for as many arguments as you want but ensure you do this wisely.

Use Functions to Organize Your Code

Functions are useful for organizing your code, making it more readable and efficient. With functions, you can break your code into smaller, reusable chunks that are easier to understand and maintain. Additionally, if you need to make changes to your code, you only need to modify the necessary function rather than the entire code base.