Announcements

We’re beginning final projects today. Your first decision: Turtle or Text? This decision is entirely subjective: which is more engaging to you? You’ll use the same language features of Python either way.
I’m going to focus on introducing Class extension and helping you get an initial project plan today. If you have Dictionaries questions that we don’t get to today, save them. We’ll have plenty of time to review as you work on final projects the rest of the semester.
Don’t Panic.
Classhack assignment is now Extra Credit, and due next week. Highly recommended for Turtlers, regular recommended for everyone else.

Q&A

Any questions or vocab?

Extending the Turtle Class

Class extension is starting from a Class that’s already defined and then setting it up in a custom way and/or teaching it how to do new things. Here’s an example extension of the Turtle class:

class BoxTurtle(turtle.Turtle):
  # Override some defaults:
  def __init__(self):
    # First, set up BoxTurtles like regular Turtles:
    turtle.Turtle.__init__(self)

    # Then, customize these things:
    self.speed(3)
    self.penup()
    self.shape("turtle")
    self.color("brown")

  # a custom method that makes `.draw_square` work on BoxTurtle objects
  def draw_square(self):
    for i in range(4):
      self.forward(100)
      self.right(90)

Understanding `self`

Each instantiated object is different, and has different characteristics. These characteristics can be accessed via dot-notation on the self object.

When you’re defining a class, self stands in for any particular object. Once you’ve created an object, you can think of it as if that were to be called on the object instead.

For instance, let’s create a BoxTurtle:

tina = BoxTurtle()

When this line of code runs, __init__ tells Python how to set tina up. As part of that, this:

    self.speed(3)
    self.penup()
    self.shape("turtle")
    self.color("brown")

…happens like this:

    tina.speed(3)
    tina.penup()
    tina.shape("turtle")
    tina.color("brown")

And so on with other BoxTurtles we instantiate.

In fact, this has already been happening with all Turtle objects you’ve ever created! So, even though it might look unfamiliar, you’re already familiar with its effects.

Methods

Methods are things certain Classes of objects can do. With Turtle ojects, you can think of them as new skills you’re teaching the Turtle.

Think _creating) methods like creating functions: you use the def keyword, except methods always get self as a parameter, and always have access to the particular object they’re being called on.

Let’s play!

Selecting a Final Project Type: Turtle or Data Processing

We’ll end the class today with a pull request containing your initial ideas. You’ll revise these ideas in a separate post due next week, and a draft of your program’s interface.

Final Project Guides.

Don’t Panic!! These are references, intended to be helpful to you. Don’t read them all for next week, but I would recommend reading the one that corresponds to your final project category, and the one on interfaces. Return to them as needed, and I’ll also refer you to them if I think somehting will be useful to you.

Dictionaries & Intro to Classes