How do class attributes, instance attributes, and bound methods work in Python?

Explains attribute lookup, shared class state, instance shadowing, and automatic method binding through practical Python behavior.

1Say itAnswer out loud first

2CompareCompare with Core answer

3RefineRefine with Stronger and Advanced

TL;DR

A class attribute belongs to the class and is shared through its instances unless an instance shadows that name. An instance attribute, commonly assigned through self in __init__, belongs to that instance. Putting a mutable list on the class can therefore make every instance see one list. A function stored on a class becomes a bound method when accessed through an instance: Python supplies that instance as the first argument, conventionally named self.

Full answer below

Practice focus

A usable Python object model that prevents shared mutable class-state bugs and explains what self represents.

Answer first

Answer path

Core answer first, then checkpoints toward a stronger answer.

Start
Core answer
Start here. This is the direct spoken answer to practice first.
Overview
Python classes hold shared attributes and functions, while instances usually hold per-object state; lookup connects the two at runtime.
A class attribute belongs to the class and is shared through its instances unless an instance shadows that name. An instance attribute, commonly assigned through self in __init__, belongs to that instance. Putting a mutable list on the class can therefore make every instance see one list. A function stored on a class becomes a bound method when accessed through an instance: Python supplies that instance as the first argument, conventionally named self.
Checkpoint
Stronger answer
Optional upgrade with examples, trade-offs, and sharper phrasing.

Review signals

Use these to catch weak phrasing, shallow reasoning, and risky claims.

Common mistakesCandidateCommon mistakesMistakes that weaken the answer or signal shallow understanding.Open details

Details

Putting a mutable collection on the class when each instance needs its own.
Saying self is a reserved keyword.
Treating a bound method as a copy of the function.
Assuming every assignment updates the class attribute.

How do class attributes, instance attributes, and bound methods work in Python?

Practice focus

Answer path

Overview

Review signals

Follow-up prompts

Continue the section

Skill areas

Suggest an improvement

Found this answer useful?