CMU CS Academy 2.21 and 2.2.2

Our first examples

We know how to create drawings. Now, let's make our drawings interactive, so they ​ (a)   . Exciting!

First, let's start with this example:

def ​ (b)   (x, y)​ (c)  

Circle(​ (d)   , ​ (e)   , 20)

Run the code. See how it does nothing. Well, it does ​ (a)   . It ​ (b)   the function onMousePress, and that function would ​ (c)   if it was ever called. Only, we never call the function. Odd.

Now, run that example again, only this time, ​ (d)   . You will see a new circle appear each time you click! That's what our example does!

The function onMousePress (x, y) is called with two ​ (a)   -- the ​ (b)   location where the mouse ​ (c)   .

Let's change the code so the radius of the circles depend on ​ (a)   the farther to the right, the bigger:

def onMousePress(x, y):

Circle(0, 200, ​ (b)   , opacity=20)

Run the code, and click the mouse several times ​ (c)   , sometimes on the right, sometimes on the left. See that a circle is always drawn centered at the point ​ (d)   but depending where we click we draw either a big or a small circle.

Why does the code set the radius to x?

We want the radius to change depending on where the mouse is (a)   .

When did we call onMousePress?

We never call onMousePress. Python calls it for us anytime we (a)   the mouse.

Basically, ​ (a)   happens. The code defines the function ​ (b)   . Then, when you click the mouse, Python tries to call ​ (c)   . Since no such function exists, ​ (d)   does nothing.

Which of the following is TRUE?