Descriptor

Fatma Kahveci
Coding
Page content
  • It lets objects customize attribute lookup, storage, and deletion.
  • Any object which defines the methods
    • __get__(self, type=None) -> object,
    • __set__(self, obj, value) -> None,
    • __delete__(self, obj) -> None, or
    • __set_name__(self, owner, name).
class Verbose_attribute():
    def __get__(self, obj, type=None) -> object:
        return 42

    def __set__(self, obj, value) -> None:
        raise AttributeError("Cannot change the value")

class Foo():
    # To use the descriptor, it must be stored as a class variable in another class.
    attribute1 = Verbose_attribute() 

my_foo_object = Foo()
print(my_foo_object.attribute1) # finds a descriptor instance, recognized by `__get__` method.

is the same:

class Foo():
    @property
    def attribute1(self) -> object:
        return 42

    @attribute1.setter
    def attribute1(self, value) -> None:
        raise AttributeError("Cannot change the value")

my_foo_object = Foo()
print(my_foo_object.attribute1)