How Does Python's @property Decorator Work, Including Its Getter, Setter, and Deleter Methods?

How Does the @property Decorator Work in Python?

The @property decorator is a powerful tool in Python that allows us to define properties for our classes. But its usage as a decorator, despite taking arguments when used as a function, can be confusing.

Property Objects

The key to understanding the decorator's behavior lies in the property() function. This function returns a special descriptor object, which has additional methods: getter, setter, and deleter.

Creating Properties with Decorators

The @property syntax is syntactic sugar for manually defining a property object. The code below is equivalent to the @property decorator usage:

def foo(self): return self._foo
foo = property(foo)

When we assign a function to a property, we replace the function with a property object.

Decorating Setter and Deleter Methods

The @property.setter() and @property.deleter() decorators, despite using the x.setter and x.deleter syntax, do not create new objects. Instead, they invoke the getter, setter, and deleter methods of the property object:

x.setter = property().setter(another_setter_function)  # Replace setter
x.deleter = property().deleter(another_deleter_function)  # Replace deleter

These methods return new property objects with the updated setter or deleter methods.

Using Descriptor Methods

Property objects act as descriptor objects with __get__(), __set__(), and __delete__() methods. These methods handle instance attribute access:

prop.__get__(instance, owner_class): # Access the property
prop.__set__(instance, value): # Set the property
prop.__delete__(instance): # Delete the property

Example

Let's build a property using the decorator methods and descriptor methods:

class PropertyDemonstrator:
    def __init__(self):
        self._private_data = 5

    def get_private(self): return self._private_data

    def set_private(self, value): self._private_data = value

    def delete_private(self): del self._private_data

    # Create a property using decorator methods
    private = property(get_private, set_private, delete_private, "My Private Data")

    # Create a property using descriptor methods
    another_private = Property(get_private, set_private, delete_private, "My Another Private Data")

In this example, the property object's descriptor methods would handle the actual manipulation of the _private_data attribute, providing a consistent and flexible way to access, modify, or delete it.

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