What is the difference between a class attribute and an instance attribute?

Question

Accepted Answer

**Class attribute** is shared between all instances. **Instance attribute** is unique to each instance.

```python
class User:
    # Class attribute (shared)
    role = "user"
    count = 0

def __init__(self, name):
        # Instance attribute (unique)
        self.name = name
        User.count += 1

u1 = User("Alice")
u2 = User("Bob")

print(u1.name)    # "Alice" (instance)
print(u2.name)    # "Bob" (instance)
print(u1.role)    # "user" (class)
print(u2.role)    # "user" (class)
print(User.count) # 2 (class)

# Changing class attribute
User.role = "admin"
print(u1.role)  # "admin" (changed for all)

# Changing instance attribute
u1.role = "moderator"
print(u1.role)  # "moderator" (only for u1)
print(u2.role)  # "admin" (unchanged)
```

Python: What is the difference between a class attribute and an instance attribute?