Class methods read-only by default?

[Emanuele D'Arrigo]

Hi Everybody!

I just tried this:
.... def method(self):
.... pass
....
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'C' object attribute 'method' is read-only

How come? Who told the class to make the method read-only? I didn't!

Manu

 

[Emanuele D'Arrigo]

Thank you both, Steven and Andrew, for the insightful explanation. I
shall keep it in mind when thinking about classes methods and
instances. Thank you again.

Manu

 

[Piet van Oostrum]

ED> Hi Everybody!
ED> I just tried this:
ED> ... def method(self):
ED> ... pass
ED> ...

ED> Traceback (most recent call last):
ED> File "<stdin>", line 1, in <module>
ED> AttributeError: 'C' object attribute 'method' is read-only

ED> How come? Who told the class to make the method read-only? I didn't!

Methods in a class are done with the descriptor protocol. All access to
the method through an instance is executed via the descriptor. The
delete calls the __delete__ method of the descriptor which isn't
implemented for functions. See
http://docs.python.org/reference/datamodel.html?highlight=descriptor#implementing-descriptors
(Actually, IIRC, the function object is its own descriptor)
.... def method(self):
.... pass
....

c=C()
C.__dict__['method']

C.__dict__['method'].__get__

C.__dict__['method'].__delete__

Traceback (most recent call last):