Whole numbers
age = 9 keeps a number you can count and add.
02TYPES + LISTS
Every box keeps something.
Picture the computer's memory as a huge shelf full of little boxes. A variable is one box with a name label on it.
WHAT GOES IN A BOX?
A box can keep different kinds of things.
Decimal numbers
height = 1.32 keeps a number with a point in it.
Text
name = "Ana" keeps letters. Text always goes between quotes.
Yes or no
is_raining = True keeps True or False. Only two choices!
age9
height1.32
name"Ana"
is_rainingTrue
Four boxes, four labels. Python finds each value by its name.
A BOX CAN CHANGE
Put in something new, and the old thing leaves.
score = 0→score = 5→score5
A box keeps one thing at a time. The newest value wins.
A BOX WITH SPACES INSIDE
A list keeps many things in order.
snacks = ["apple", "cookie", "grapes"] puts three things in one box, each in its own little space.
snacks=
- "apple"0
- "cookie"1
- "grapes"2
Python starts counting at 0. snacks[0] is the first space.
Fun fact: In math, a row of numbers in order, like [3, 1, 4], is called a vector. In Python, we make it with a list.
A SHELF OF ROWS
A matrix has rows and columns.
board = [[1, 2, 3], [4, 5, 6]] is a list of lists: two rows with three spaces each, like an egg carton.
board=
01201231456
board[1][0] means row 1, then space 0. That is 4.
RUN IT
Open the snack box.
Guess first. Then run real Python and check.
Guess the result
snacks = ["apple", "cookie", "grapes"]
print(snacks[0])What will Python show?
OUTPUT
PyBot's hint
Ready. Press Run Python.
Python runs here thanks to Pyodide ♥
Pyodide 314.0.3 runs CPython in your browser with WebAssembly.
Open-source under the Mozilla Public License 2.0. License
Now change one thing: Change 0 to 2. Which snack comes out? Then add your favorite snack to the list.
YOUR TURN
Look inside the boxes.
Try each tiny question. A wrong answer becomes something to review.
0Completed
7Not tried
0Review
Find the text box
PyBot wrote 9 in three different ways.
Which box keeps text?
What kind of thing?
is_happy = TrueWhat does this box keep?
Count the spaces
colors = ["red", "blue", "green"]How many spaces does this list have?
Count the rows
board = [["X", "O"], ["O", "X"]]How many rows does this matrix have?
Find the decimal
PyBot measured nine and a half centimeters.
Which box keeps a decimal number?
Fix PyBot's code
PyBot wants the grape. Remember: the first space is number 0.
Goal output
grapeOUTPUT
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BIG IDEA
A variable is a labeled box in memory.
It can keep a number, some text, a yes or no, or even a whole list.