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How to call a function in Python

This post explains how to use a Python function call, how to pass variables.

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Published onApril 10, 2021

In the last post introducing Python, I demonstrated how to make a simple app using variables and conditional statements. In order to do anything really powerful in a given programming language though, you need to understand functions! In this post, we’ll discuss the Python function call.

What is a Python function call?

Before we look at how to call a function in Python, we first need to familiarize ourselves with the concept.

Also read: Best online Python courses

Functions are used throughout programming as a way to group certain tasks together. This becomes useful in a variety of circumstances, particularly when a repetitive task needs to be carried out multiple times.

Functions are used throughout programming as a way to group certain tasks together.

For example, if you built an app that drew hundreds of triangles on the screen to generate a kaleidoscopic effect, you could do this in one of two ways:

Without functions: by repeatedly writing the code to draw a triangle with.
With a Python function call: by generating lots of coordinates and feeding them to your “draw triangle” function.

The latter is far more efficient, requires less code, and is generally the preferred method. Not only that, but if you ever decide you want to draw squares instead of triangles; you could change just a few lines of code and the entire output would be different!

One more benefit of using functions is that they are modular and portable. If you write another program with a triangle in it, you can just copy and paste your triangle code wholesale!

Python call function example

Here is an extremely simple example of a Python function that will print “Hello World!” onto the screen:

Code

def hello_print():

    print("Hello World!")

    return

hello_print()

That is how to define a function in Python and call it!

The function here is called HelloPrint. First we “define” this function with the def statement, then we place any code we want to be a part of it directly beneath. The return statement simply instructs the interpreter to return to whatever point in the code it was at before it carried out the function.

Note that I’ve capitalized each word in my function name. This is a good practice as it helps to distinguish a Python function call from statements.

Now, any time we want to say “Hello World!” we can simple write HelloPrint() and it will happen!

For example:

Code

def hello_print():

    print("Hello World!")

    return

hello_print()

hello_print()

Run this code and you’ll now see the “Hello World!” message appear twice!

Because this code is grouped separately, it won’t run until you use the Python function call. That also means that this code will do the precise same thing:

Code

def hello_print():

    print("Hello World!")

    return

hello_print()

hello_print()

This also means you should be able to figure out how to call a function from another function:

Code

def greetings_print():

    print("Hello World!")

    nice_day_today()

    return

def nice_day_today():

    print(“Nice day today, isn’t it!”)

    return

greetings_print()

And that, in a nutshell, is how to call a function in Python! But we still haven’t tapped into the real power of Python functions yet!

How to pass information to a Python function call

While functions are useful for performing repetitive tasks, their real power lies in the ability to give and receive data. This is what those little brackets are for: they allow us to call a function in Python while also passing in data.

For example, the following code will say “Hello Adam”:

Code

def say_hello(Name):

    print(“Hello ” + Name)

    return

say_hello(“Adam”)

This is means that the same function can perform slightly different actions depending on the variables we give it.

How to manipulate data

Even more useful though, is the ability of a function to transform data.

To do this, we need to pass information into the function, perform an action, and then return that information.

Here’s one way that we might perform this with a Python functional call:

Code

def multiplier(Number):

    return = Number * 10

print(multiplier(5))

Here, the output will be “50” because the number 5 is passed with the Python function call, which returns that value multiplied by 10. Notice how we can write the Python function call just as though it were the name of an integer itself. This allows for very rapid and flexible coding!

There are countless ways we can use this feature. Here is another little example that requires just three lines of code:

Code

def counter(Name):

    return len(Name)

name_please = input("Name length counter! Enter your full name ")

print(Counter(name_please))

This little app is a “name length counter.” This uses the len statement from Python, which returns an integer based on the length of a string. So, this fun app can tell you how many characters are in your name!

That’s including spaces but hey, no one is perfect.

We’re just scratching the surface of Python can do

Now you know how to use a Python function call! This opens up a world of possibilities, but don’t stop there! To really flex the full power of Python, you’ll need to understand concepts such as functions, modules, and more. To that end, we recommend checking out our guide to the best online Python courses.

That said, if you’re a true beginner and looking for a great course that’s easy to get started with, we highly recommend Coding with Python: Training for Aspiring Developers, which you can nab for just $49.99, which is an absolute steal as the course is valued around $700.

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