APCSP Unit 3

A variable is an abstraction inside a program that can hold a value. Each variable has associated data storage that represents one value at a time, but that value can be a list or other collection that in turn contains multiple values.
An index is a common method for referencing the elements in a list or string using natural numbers.
An element is an individual value in a list that is assigned a unique index.

A group is a collection of shapes we treat as a single shape.
g = Group(shape1, shape2, shape3) makes a group with three shapes.
g.centerX += 5 will move every shape in the group to the right by 5.
Make sure each shape in the group is separated by a comma, and you have both parentheses.

Only the following properties work with groups.
centerX and centerY refer to the center of the group.
right, left, top, and bottom refer to the edges of the group if you drew a box around every shape in the group.
fill, opacity, visible will change these properties for every shape in the group.
rotateAngle rotates the entire group around the center of the group.
group.children is a list of every shape in the group.

If you want to do the same thing to every shape in a group, loop through group.children.
for shape in group.children: lets you access the properties of each individual shape.
Test shape.hits(mouseX, mouseY) in a loop to see which shape in a group is hit.
If a shape in the group is made invisible, it is removed from the group!

Global variables are defined outside of functions, and can be used anywhere in your code below the line where you define your variable.
Only use globals when storing shapes or groups that you want to change later.

Function parameters are local variables.
Locals can only be used within the function in which it is defined.
Helper variables are a useful kind of local variable that make your coded easier to read.
Using a color variable might help you set the color of multiple shapes to the same thing.
Use locals as much as you can!
Do not name them the same thing as a global variable.

Lists can store multiple values like colorList = ['red', 'green']
group.children is a list.
for color in colorList: will loop through each color in the list, assigning it to color.
Indexing into a list is how you access elements of the list without a loop.
- Indices start at 0!
- colorList[0] is 'red'
- colorList[1] is 'green'
- colorList[2] causes an out of bounds error! (there are only two elements)
colorList[0] = 'purple' changes colorList to ['purple', 'green']

You need a counter for your index which goes back to 0 when you reach an invalid index.
Use the mod operator! % is a remainder operator. (4 % 3 is 1)
counter % length of list will never be out of bounds, and rotates through the indices.

If we have a list like colorList = ['red', 'red', 'yellow'] we can use these methods:

colorsList.append('green') puts 'green' at the end.
- → ['red', 'red', 'yellow', 'green']
colorList.insert(1, 'orange') inserts 'orange' at index 1.
- → ['red', 'orange', 'red', 'yellow', 'green']
colorList.remove('red') removes the first 'red' from the list.
- → ['orange', 'red', 'yellow', 'green']
colorList.pop(2) removes the element at index 2.
- → ['orange', 'red', 'green']
AP Exam: APPEND and INSERT are the same on the AP Exam, but REMOVE works like pop()

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