After this lesson, you will be able to:

• Define a class and create separate objects from it.
• Attach, read, and update attributes belonging to an individual object.
• Define an instance method and access the current object through self.
• Change an object's state from inside an instance method.

If you have used classes in Java or C#, Python's basic idea will be familiar: a class defines a type of object, and an instance is one particular object of that class. Python uses a colon and indentation rather than braces:

class Server:
    pass

For now, pass gives the class a valid, empty body. Create an object by calling the class name: server = Server(). You can attach fields, called attributes, directly to that instance with dot notation: server.region = "eu". Two instances can hold different values without affecting each other.

A method is a function written inside a class. An instance method declares self as its first parameter. When you call server.label(), Python passes server as self automatically. Inside the method, self.region means the region of the particular object receiving the call. Methods can also update instance attributes.

For this first lesson, we assign attributes after creating each object so that you can see the object model clearly. In the next lesson, __init__ will show how to initialize attributes when an object is created. We will cover class attributes and inheritance later.

1. Create two independent objects

An empty class is enough to create instances and attach different values to each one.

class Endpoint:
    pass

public = Endpoint()
public.path = "/public"

internal = Endpoint()
internal.path = "/internal"

print(public.path)
print(internal.path)

Output:

/public
/internal

The two path attributes belong to different objects.

2. Read instance attributes from a method

The same method can return a different result for each instance because self refers to the object that called it.

class Printer:
    def label(self):
        return f"{self.name} ({self.region})"

first = Printer()
first.name = "labels"
first.region = "eu"

print(first.label())

Output:

labels (eu)

The method uses the attributes attached to first.

3. Let a method update the current instance

A method can change an attribute through self. This change stays with that object.

class Counter:
    def record(self):
        self.total += 1

counter = Counter()
counter.total = 0
counter.record()
counter.record()

print(f"Total: {counter.total}")

Output:

Total: 2

The total attribute was created before record() used it. The next lesson will make that setup more reliable.

1. Missing self in a method: normal instance methods need it as their first parameter.
2. Using a bare attribute name inside a method: write self.name, not just name, to read that instance's attribute.
3. Assuming objects share changes: setting first.status does not change second.status.
4. Accessing an attribute before assigning it: without a constructor or earlier assignment, it may raise AttributeError.