Functions in Python: Way to reuse and structure your code

A function in Python is a block of operations performed when the function is called. The function can take input parameters and use these to make calculations. Functions can also return values when the function is executed.

Functions in Python

By writing your code as functions, you can easily reuse the same code several times in different places in the program. This chapter goes through how to create and use functions with the following articles

• Introduction: Functions (this article)
• Create a function
• Call a function
• Summary: Functions in Python

What is a function in Python?

A significant advantage of functions in python is that you do not need to write the same code multiple times. You can call the function instead. A function is a block of operations that are performed when called. This means that instead of rewriting the same code several times, we can instead reuse code that is run multiple times, in different places in the program. A function can get one or more values, so-called input parameters, and can also send back, return one or no value. By return is meant what the method “returns” when it has performed the operations it contains. A method is always terminated when a value has been returned.

A function in Python performs a sequence, a block of operations when the method is called.

Functions are a very powerful tool because they are entirely independent of other code and can be called from other functions if desired. The uses of functions are many, and they help to structure and simplify the programs we create.

You can imagine a functions like a black box.

• First, you send one or more values into the box and get another one, but you do not need to know what is actually happening in the box, how the code is programmed.
• The important thing is that you know what happens when the function is called.
• This abstracts the program and creates a more compact program.

How functions in Python work? 

A function in Python can be structured in a couple of different ways. On the one hand, you can choose whether the function should take in information, in other words, if the function should take any input. But also what should come out of the function, quite simply, what the function returns and what will be the result when we use the function. 

Therefore, in general, we can say that we need to state two things when we create the function:

1. Number of input parameters. It can be anything from no input parameters to several different input parameters.
2. What the function returns. Similar to the input parameters, we can state that the function should return a value, or that it simply does not return anything at all.

If we illustrate the different alternatives of methods

When should I use a function in Python?

• Reusable code: If you need to do the same thing (or almost the same thing) many times over, write a function to do it, and then use that function every time you perform that task. 
• Top-down programming: A beneficial approach in programming is called top-down programming. You solve a big problem, which is seen as the “top”, by breaking it down into smaller problems. 
• Visualize the problem: Use function to break down the task in your mental picture of the problem, making it much easier for you to work with your programs if you break them down and try to visualize them in smaller parts. 
• Simplify: Sometimes, we do not need to know how a function works; we are only interested in what it does. This means that, as mentioned earlier, we can focus on the main problem and focus on what our function produce, rather than how they do it.

To summarize, in this chapter:

• We will first discuss in detail how a function works and why we use it
• Additionally, we will go look at different types of functions and what you need to consider when returning values
• Finally, the chapter ends with a few examples where you get the opportunity to create a couple of functions.