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14OBJECTS · THE MOLD

Make your own mold with class.

A class is a mold. It says what every robot made with it will know. Then you use it to make real robots.

IN REAL LIFE

A mold is not the thing.

A mold is the plan. You use it to make the real things.

A cookie cutter

The cutter is not a cookie. You use it to make cookies.

An ice tray

The tray has the shape. Water goes in, ice cubes come out.

A blank form

Every form asks for a name. Each person writes their own.

LOOK FIRST

Three new words, one at a time.

class

class Robot: starts the mold. Mold names start with a capital letter.

init

The mold's setup job. It runs by itself each time a new robot is made. Two _ before and two after.

self

self means “this robot itself”. self.name = name writes the name inside this robot.

STEP BY STEP

Read the mold line by line.

Take it slow. The first 4 lines are only the plan. Line 5 makes a real robot.

class Robot:Starts the mold called Robot. No robot exists yet.

def __init__(self, name):The setup job. It gets the new robot (self) and a name.

self.name = nameWrites the name inside this robot.

self.battery = 100Every new robot starts full: 100.

bolt = Robot("Bolt")Use the mold! Now a real robot exists. You do not write self: Python fills it in.

print(bolt.name)Read its data with a dot: Bolt

print(bolt.battery)Shows 100

Remember the turtle? turtle.Turtle is a mold too. t = turtle.Turtle() used it to make one turtle.

RUN IT

Make your first robot.

Guess first. Then run real Python and check.

Guess the result

class Robot:
    def __init__(self, name, color):
        self.name = name
        self.color = color

rita = Robot("Rita", "green")
print(rita.name)
print(rita.color)

What will Python show?

robot.pyREAL PYTHON

OUTPUT

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 "green" to your favorite color. Then add: print(rita.name, "is", rita.color)

YOUR TURN

Mold or robot?

Try each tiny question. A wrong answer becomes something to review.

0Completed

8Not tried

0Review

Like a class

A class is the plan to make things, not the thing.

Which one is like a class?

Start the mold

Which line starts a mold the right way?

Only the mold

class Cat:
    def __init__(self, name):
        self.name = name

How many cats exist after this code?

A real cat

class Cat:
    def __init__(self, name):
        self.name = name

tom = Cat("Tom")
print(tom.name)

What does Python show?

Who is self?

Inside the mold, what does self mean?

Full battery

class Robot:
    def __init__(self, name):
        self.name = name
        self.battery = 100

zap = Robot("Zap")
print(zap.battery)

What does Python show?

Fix PyBot's code

PyBot made a robot but forgot its name. The mold needs a name inside the ( ). Make it show: Pip

PyBot's code

Goal output

Pip

OUTPUT

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BIG IDEA

A class is a mold. An object is a thing made with it.

class names the mold, __init__ sets up each new robot, and self means “this robot”. Next: many robots from one mold!