Why has __new__ been implemented as a static method?

[Steven D'Aprano]

On Sun, 04 May 2014 11:21:53 +1200, Gregory Ewing wrote:

> Steven D'Aprano wrote:
>> I'm not entirely sure what he means by "upcalls", but I believe it
>> means to call the method further up (that is, closer to the base) of
>> the inheritance tree.
> 
> I think it means this:
> 
>     def __new__(cls):
>        MyBaseClass.__new__(cls)
> 
> which wouldn't work with a class method, because MyBaseClass.__new__
> would give a *bound* method rather than an unbound one.

If it were a class method, you would call it by MyBaseClass.__new__() 
rather than explicitly providing the cls argument.


> Python 3's version of super() seems to work with class methods, but
> Python 2's doesn't (or at least I couldn't get it to work in a brief
> test). 

Works for me. Perhaps you got your super() call wrong?

py> class MyDict(dict):
...     @classmethod
...     def fromkeys(cls, *args, **kwargs):
...             print "Calling overridden method."
...             return super(MyDict, cls).fromkeys(*args, **kwargs)
...
py> MyDict.fromkeys('abc')
Calling overridden method.
{'a': None, 'c': None, 'b': None}
py> MyDict().fromkeys('abc')
Calling overridden method.
{'a': None, 'c': None, 'b': None}


> Also, I don't think super() existed at all when __new__ was
> invented.

Well, I don't know about that, but super was introduced in the same 
version as new-style classes with __new__.



-- 
Steven D'Aprano
http://import-that.dreamwidth.org/