Modules -> OOP -> Classes and objects -> Instances as attribute values

Instances as attribute values

Pre code

class Dog:
    """Represents a dog.

    attributes: name, age and collar
    """

class Collar:
    """Represents a collar.

    attributes: color and size
    """

An object attribute can store another object as its value. For example, a dog can have a collar.

We have two classes: Dog and Collar. The Dog class will include an attribute named collar, which will be an instance of the Collar class.

...
strap = Collar()
strap.color, strap.size = 'blue', 4

dog = Dog()
dog.name, dog.age = "Murki", 2
dog.collar = strap

strap is an instance of Collar, which has a color and size. dog has an attribute collar and its value is strap.

...
>>> dog.collar
<Collar object at 0x00000148DF521010>
>>> dog.collar.size
4

The expression dog.collar.size means, "Go to the object dog refers to and select the attribute named collar; then go to that object and select the attribute named size."

We can create a Collar object and directly assign it to dog's collar attribute:

...
>>> dog.collar = Collar()
>> dog.collar.size = 5
>>> dog.collar.color = 'black'
>>> dog.collar.size
5

Exercises

Create two classes, Book and Author.

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Create an author, writer, with name and age attributes

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Create a book, novel, with title: str, pages: int and author: Author attributes.

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►

Create two classes, Artist and Painting.

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Create an artist, with name: str and painting: Painting attributes

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Create one class, Dog.

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Create a dog, dad, with name: str attribute

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Create a dog, puppy, with name: str and parent: Dog attributes

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Create classes Book, Cover, and Publisher.

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Create a cover, cv with color attribute.
Create a publisher, pb, with name attribute.

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Create a book, bk, with cover: Cover and publisher: Publisher attributes

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class Person:
    """Represents a person.

    attributes: name, best_friend
    """

p1 = Person()
p1.name = "Arta"

p2 = Person()
p2.name = "Zana"
p2.best_friend = p1

Given the above script:

What is type of p2.best_friend:
What is value of p2.best_friend.name:

Exercises

Create two classes, Backpack and Student.

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Create a backpack, bp, with color attribute

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Create a student, st, with name: str, grade: int and bag: Backpack attributes.

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Create two classes, Bird and Nest.

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Create a bird, with species: str and nest: Nest attributes.

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Create one class, Animal.

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Create an animal, a1, with name: str attribute

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Create an animal, a2, with name: str and friend: Animal attributes

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Create classes Movie, Director, and Actor.

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Create a director, d with name attribute.
Create an actor, a, with name attribute.

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Create a movie, m, with title: str, director: Director and main_actor: Actor attributes

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class House:
    """Represents a house.
    
    attributes: owner, address
    """

class Owner:
    """Represents a house owner.
    
    attributes: name
    """

class Address:
    """Represents an address.
    
    attributes: street
    """

person = Owner()
person.name = "Blerina"

addr = Address()
addr.street = "Rr. Iliria"

h = House()
h.owner, h.address = person, addr

Given the above script:

What is type of h.owner:
What is value of h.owner.name: