What are slots in Python?

Question

Accepted Answer

**__slots__** — restriction of instance **attributes**.

```python
class User:
    __slots__ = ("name", "age")

def __init__(self, name, age):
        self.name = name
        self.age = age

user = User("Alice", 25)
# user.email = "a@b.com"  # Error! Not in __slots__

# Memory savings
import sys

class WithSlots:
    __slots__ = ("x", "y")

class WithoutSlots:
    pass

a = WithSlots()
b = WithoutSlots()
print(sys.getsizeof(a))  # Less!
print(sys.getsizeof(b))  # More!

# Inheritance
class Admin(User):
    __slots__ = ("role",)  # + parent slots
```

**Advantages:**
- Memory savings.
- Fast access.
- Protection from accidental attributes.

**Disadvantages:**
- Cannot add new attributes.
- Harder to debug.

Python: What are slots in Python?