Classes

A class is a blueprint and an object is a thing built from it. __init__ runs when an object is created and stores its data on self:

class Dog:
    def __init__(self, name, age):
        self.name = name
        self.age = age

rex = Dog("Rex", 3)
rex.name   # "Rex"

self is the new object, passed automatically to the method. Store persistent attributes with self.name = name; assigning only name = name does not store anything on the object. Arguments to Dog("Rex", 3) supply name and age, not self.

The Visualizer shows each object as a card with its attributes.

See it run

class Dog:
    def __init__(self, name):
        self.name = name
        self.tricks = 0

rex = Dog("Rex")
fido = Dog("Fido")
rex.tricks = 2
print(rex.tricks, fido.tricks)

The class is the blueprint. Each Dog(...) builds a separate object on the right.

Practice classes

Exercise 1

Create a class Pet whose __init__ takes name and species and stores both. Then make my_pet = Pet("Rex", "dog").

Exercise 2

Create Parcel(label, weight, fragile=False) storing all three attributes per instance. Make box = Parcel("Books", 4) and glass = Parcel("Vase", 1, True).

Exercise 3

Create Reading(sensor, values) storing sensor and an independent list copy of values. Make raw = [12, 14] and sample = Reading("roof", raw), then append 99 to raw. The reading must retain its original snapshot; separate readings must not share lists.

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Practice

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Visualizer Watch your code run line by line

Run your code, then choose Play to follow its execution.

Memory · names → values

Variables appear here as Python creates them.

Output & plots