Functions

Code sample link: https://replit.com/@jjoco/python-functions

Functions are like any mathematical function: you put something in, the function does something with your input, and you get something out. In Python, the keyword for defining a function is def, followed by a function name with parameters.

Defining a function

def function_name(input1 , ...):
   # Do stuff

Function inputs and outputs need not have type hints; however, it is generally good code convention to have types hinted, anyway:

def function_name(input1: type1 , input2: type2 ...) -> return_type:
   # Do stuff

Calling a function

To call a function, use the following syntax

function_name(input1, input2)

What this is doing is invoking a function to do work on the given inputs. If the function is set to return some output, then the calling function can retrieve the output value like so:

var_1 = function_name(input1, input2)

Then, the dev can use the value set in var_1 to do whatever they want.

Let's go through a more concrete example. Let's say I wanted to create a function that doubled the original value inputted. It's obviously bad practice to have a function name be something vague like

def a():
    #Do stuff

It is very good coding practice to be precise with your function names, especially in bigger projects. Let's implement the doubling function:

def double(x):
    return x*2

We take an input x value and return x multipled by two. We can call double somewhere else, like the following:

doubled = double(5)
# doubled == 10

For those wondering, you can call a given function within itself:

def some_function(x):
    .
    .
    .
    some_function(x)

This is called a recursive function, in which a function calls itself at some point within its implementation. However, I will not be going over these type of functions in this tutorial.