More Conditionals, Key Events, and Methods in Python

This week we are covering More Conditionals, Key Events, and Methods in Python. Once again we will code using CMU Academy IDE (Integrated Development Environment). CMU CS Academy is an online, graphics-based computer science curriculum taught in Python provided by Carnegie Mellon University. They create novel, world-class Computer Science education forthe classroom —and it’s entirely free. You can sign up for it here: CMU CS Academy

Alternatively, To get started in Python, I also recommend getting PyCharm: https://www.jetbrains.com/pycharm/

In each blog post, I will go over some examples, creative tasks that I created, related code and summarize the key concepts and syntax we learned .

Now here’s how I created this animated vintage Space Invaders Python code :

Here’s the concept summary for this week:

More Conditionals(if-elif-else Statements)

if-elif-else Statements

• After we use if, we can use elif to add another test that will only be tested if the first test was False

  • Note that elif is actually short for else if

• There can be many elif's following an if, but at most one of their bodies will run

• Use elif without else, but you cannot use elif without if

• Code in an else body runs if all the tests before it were False

• else can be thought of in English as "otherwise"

Key Events

onKeyPress and onKeyRelease

• onKeyPress is called when a key is pressed

• The parameter to onKeyPress is key

• Use the key parameter to test which key was pressed using if and elif statements

• Use onKeyRelease to run code when the user releases a key

• The arrow keys are represented as: “left”, “right”, “up” and “down”

Methods

Custom Properties

• Can add your own custom properties to any shape

  • Ex. For a circle c, can initialize c.count = 0, and then can use that count throughout

• Must be named something not used by CMU Graphics already

• Can also have custom app properties that do not belong to a shape

Shape Methods

• toFront() brings a shape to the front of other shapes

• toBack() pushes a shape to the back of other shapes

• Methods are basically the same as functions, with these two differences:

  • Methods are called differently: We use shape.toFront() instead of toFront(shape)

  • Methods are like properties in that they can differ across shapes

  • Every shape has the toFront() and toBack()

• addPoint(x, y) is only available for polygons

  • Takes the (x, y) values of some point on the canvas, and adds that point to the polygon

• contains(x, y) takes two values, x and y, and simply tells us whether or not the shape contains the point (x,y)

  • returns True or False

• shape.hits(x, y)

  • If the fill=None for the shape, any point inside the shape will return False

• shape1.hitsShape(shape2) tests if a shape hits another shape

• shape1.containsShape(shape2) tests if the first shape fully contains the second shape

• app.stop() is called when we want no more events happen

I hope this helps.

Till next post, happy coding,

Alara