Functions are an essential part of programming, as they can execute a block of code at once. Often it's an excellent way to re-use blocks of code.

Let's give it a go and see how they work in Python.

Creating a function in Python

A function is made by prefixing the def keyword.

def foo():
    print("Bar")

However, running our code now will not do anything since we didn't call our function yet.

Executing the function

To run/execute the function, we must call it somewhere in our code. In general, this happens when a specific criterion is matched, but let's just run it as is.

def foo():
    print("Bar")

foo()

When we run our code now, it returns Bar

Passing and returning data

Having a function that prints out something is not convenient so let's see how we can give it data and return something.

Let's say we want to make a function that multiplies a number by itself and returns the output.

Meaning, if we put in the number 5, it should run 5x5 and return 25.

def multiply(number):
    return number * number

print(multiply(5))

Running this code will indeed return 25.

We can easily have the function accept multiple arguments like so:

def multiply(number, multiplier):
    return number * multiplier

print(multiply(5, 10))

This will return 50.

And one cool thing we can do is send the arguments based on their key value like this.

multiply(number=5, multiplier=2)

You might not know how many arguments you're expecting in some cases, and you can prepend the argument with an asterisk (*).

def feed_animals(*animals):
    print(animals)
    print(animals[1])

feed_animals('Cow', 'Chicken', 'Goat')

Which will return:

('Cow', 'Chicken', 'Goat')
Goat

There are some more additions to functions, but this covers the basics for Python functions.

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