Class attributes in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a class attribute in Python?

A class attribute is a variable that is shared by all instances of a class. It is defined inside the class but outside any instance methods.

beginner

How do class attributes differ from instance attributes?

Class attributes are shared by all instances of the class, while instance attributes belong to each individual object and can have different values.

beginner

Given this code:<br><pre>class Dog:
    species = 'Canis familiaris'
    def __init__(self, name):
        self.name = name</pre><br>What is <code>species</code> here?

<code>species</code> is a class attribute. It is shared by all Dog objects and holds the value 'Canis familiaris'.

intermediate

Can you change a class attribute value for all instances? How?

Yes, by assigning a new value to the class attribute using the class name, e.g., <code>ClassName.attribute = new_value</code>. This changes it for all instances that don't override it.

intermediate

What happens if you assign a value to a class attribute name using an instance?

Assigning a value to a class attribute name via an instance creates or changes an instance attribute with the same name, which hides the class attribute for that instance only.

Where are class attributes defined in Python?

A Inside the class but outside any methods

B Inside instance methods only

C Outside the class definition

D Inside the __init__ method only

Class attributes are defined inside the class but outside any instance methods.

What is shared by all instances of a class?

A Instance attributes

B Local variables

C Class attributes

D Function parameters

Class attributes are shared by all instances, while instance attributes are unique to each object.

If you change a class attribute using the class name, what happens?

A All instances see the updated value unless they have an instance attribute with the same name

B Only the first instance changes

C Nothing changes for any instance

D Only new instances get the change

Changing a class attribute via the class name updates it for all instances that do not override it.

What happens if you assign a value to a class attribute name using an instance?

A The class attribute changes for all instances

B An instance attribute is created or updated, hiding the class attribute for that instance

C An error occurs

D The class attribute is deleted

Assigning to a class attribute name via an instance creates or updates an instance attribute, hiding the class attribute.

Which of these is a correct way to access a class attribute?

A ClassName.__init__()

B instance.attribute()

C instance.__init__()

D ClassName.attribute

Class attributes are accessed using the class name followed by the attribute name.

Explain what a class attribute is and how it differs from an instance attribute.

Think about a property all objects share versus something unique to each.

Describe what happens when you assign a value to a class attribute name using an instance.

Consider how Python handles attribute lookup and shadowing.