# Instance vs Class Attributes — Python Fundamentals: From Basics to Async

Source: https://www.skillbyai.com/en/python/py-instance-class-attrs

> Tell instance attributes from class attributes, and avoid surprises when changing shared class data.

## Two kinds of attributes

**Instance attributes** (set via `self.x = ...`) differ per object. **Class attributes** are defined on the class and shared by every instance.

```python
class Dog:
    species = "Canis familiaris"   # class attribute

    def __init__(self, name):
        self.name = name              # instance attribute

a = Dog("Rex")
b = Dog("Fido")
print(a.species, b.species)  # same for both
print(a.name, b.name)        # different
```

## Careful with mutation

Changing a class attribute through the **class** (`Dog.species = ...`) affects all instances; setting it on **one instance** (`a.species = ...`) only shadows it for that object.