On 19/10/2023 18.29, Dom Grigonis wrote:
def __get__(self, instance, owner):
def __set__(self, instance, value):
Is there a reason why `__set__` does not have owner in it’s arguments
while `__get__` does?
Is this a Python Idea?
You may have only given us a couple of lines, when the scope of the
question is much wider...
Be careful because these mechanisms were updated relatively-recently -
and thus there are differences between Python versions!
From my notes (please see code-example which appears to answer your
question):
The __set_name__() method is a special method in Python that is used in
the context of descriptors. It was introduced in Python 3.6 as a part of
the Descriptor Protocol.
The purpose of the __set_name__() method is to allow descriptors to
automatically determine and store the name of the attribute they are
assigned to within the class. This method is called once during the
creation of the descriptor instance, and it receives two arguments: the
owner class and the name of the attribute.
By implementing the __set_name__() method in a descriptor, you can
access and store the name of the attribute to which the descriptor is
assigned. This can be useful when you want to associate the descriptor
with the attribute name or perform any additional setup based on the
attribute name.
Here's an example to illustrate the usage of __set_name__():
```python
class Descriptor:
def __set_name__(self, owner, name):
self.name = name
def __get__(self, instance, owner):
if instance is None:
return self
return instance.__dict__.get(self.name)
def __set__(self, instance, value):
instance.__dict__[self.name] = value
class MyClass:
attribute = Descriptor()
obj = MyClass()
obj.attribute = 42
print(obj.attribute) # Output: 42
```
In the above code, the Descriptor class defines the __set_name__()
method. When the attribute descriptor is assigned to the attribute
attribute of the MyClass class, the __set_name__() method is
automatically called with the owner class (MyClass) and the attribute
name (attribute). Inside this method, we store the attribute name in the
descriptor instance.
Later, when we set obj.attribute = 42, the descriptor's __set__() method
is called, and the value is stored in the instance's __dict__ attribute
using the previously stored attribute name.
By using __set_name__(), descriptors can dynamically associate
themselves with the attribute names they are assigned to, providing more
flexibility and customization.
Web.Refs:
https://docs.python.org/3/howto/descriptor.html
https://docs.python.org/3/reference/datamodel.html#descriptors
--
Regards,
=dn
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