Objects — Instances, Memory, and Many Values from One Class

An object is an instance of a class. Creating it allocates memory for that instance so you can store data and call methods.

Use the playground at the bottom of this page, then take the quiz.

What you will learn

• The definition of an object
• The two creation forms
• How a class and an object differ
• Why a missing class raises NameError

The picture

The purpose of an object is to store data. Processing that data starts by creating the object. If the class has not been defined, creation raises NameError.

first = Badge()
second = Badge("Avery Lane")

The first form fits a class whose constructor needs nothing beyond self. The second form passes values into that constructor.

	Class	Object
What it is	Data members and methods	An instance of that class
Memory for fields	Not allocated by the class statement	Allocated when you create the instance
How many	The definition exists once	Many objects can come from that one definition
Order	Loaded first	Created after the class exists

The same method can run on each object, and each object keeps its own fields.

Example

class Badge:
    def __init__(self, m):
        self.label = m

    def introduce(self):
        return "Hello, " + self.label

first = Badge("Avery Lane")
second = Badge("Jordan Hale")
print(first.introduce())
print(second.introduce())
print(first is second)

Both objects share the Badge methods. They do not share the label. first is second is false because they are two instances. The playground prints both greetings.

Key takeaways

• An object is an instance: memory for the class members

• Create it with ClassName() or ClassName(values)

• One class can produce many objects

• A missing class name raises NameError

• Next: Constructors — fill the object at the moment it is created

• Previous: Inside a Class