What is a data descriptor vs non-data descriptor?

Question

Accepted Answer

**Data descriptor** defines both `__get__` and `__set__`. **Non-data descriptor** only defines `__get__`.

```python
# Data descriptor (takes priority over instance dict)
class DataDescriptor:
    def __set_name__(self, owner, name):
        self.name = name

def __get__(self, obj, objtype=None):
        if obj is None:
            return self
        return obj.__dict__.get(f"_{self.name}")

def __set__(self, obj, value):
        obj.__dict__[f"_{self.name}"] = value

# Non-data descriptor (instance dict takes priority)
class NonDataDescriptor:
    def __set_name__(self, owner, name):
        self.name = name

def __get__(self, obj, objtype=None):
        if obj is None:
            return self
        return lambda: f"from {self.name}"

class MyClass:
    data = DataDescriptor()
    non_data = NonDataDescriptor()

m = MyClass()
m.data = 42         # Uses descriptor
print(m.data)       # 42 (from descriptor)
m.non_data = 42     # Stored in instance dict
print(m.non_data)   # 42 (from instance dict)
```

**Priority:**
- **Data descriptor** > instance dict.
- Instance dict > non-data descriptor.
- `property` is a data descriptor.

Python: What is a data descriptor vs non-data descriptor?