Functions

MPDA’22

December 23, 2021

What is a function?

A function is a block of code which only runs when it is called.

Calling a function just means to use a function in your code.

We’ve been using funcions during the entire course:

range(3,9)
math.cos(2*math.pi)
math.sin(math.pi)
abs(-1)
ptA.DistanceTo(ptB)
interval.ParamterAt(0)
curve.ClosestPoint(ptA)
cross = rg.Vector3d.CrossProduct(...)
surf = rg.Surface.CreateByCorners(...)

You can pass data, known as parameters, into a function.

A function can return data as a result.

Creating a function

You can create a function by using the def keyword, followed by the name and the (optional) inputs surrounded by parenthesis.

def myFunction():
    print("Hello from inside myFunction!")

Inside the indented block you can add any code you wish.

And use it like this:

myFunction()

A function can optionally have input parameters (variables)

These parameters can be of any type.

def addNumbers(a,b):
    addition = a + b
    print(addition)

# And use it placing the values inside the parenthesis
addNumbers(4, 2.3)

A function can also return data

def addNumbers(a,b):
    addition = a + b
    return addition

result = addNumbers(3,44)
print(result)

The return value can be saved into a variable for later use.

Why should you use them?

Functions are useful in many ways:

to abstract the logic into understandable pieces.
to re-use code in multiple parts of your application.
to simplify the logic of your application

Essentially, a python function is the equivalent of a grasshopper node:

They each have independent inputs that can vary
They each perform a specific operation, and have a descriptive name.

There’s only one main difference between them:

A python function can only have one return value

What does having only one return value? even mean?

It means that the result of any function has to be a single item (or no item at all).

If you need to output more than one item, you can output a list/tupple or dictionary that collects the multiple items you want to send.

def multipleOutput():
    return ["a", "b", "c"]

Recursivity

What is recursivity?

According to wikipedia, recursive is something that involves the repeated application of a rule, definition, or procedure to successive results.

🤔 🤔 🤔

In other words:

Recursive is any operation that you repeat over and over using the result from the previous iteration.

In programming, a function is recursive if it calls itself.

def power(num, exp):
    if(exp >= 1):
        return num
    return num  * power(num, exp - 1)

def countdown(start):
    if(start != 0):
        print(start)
        countdown(start - 1)
    else:
        print("BOOM!")

Meaning, that inside the function’s code you are using the same function you are creating.