Bug? If not, how to work around it?

[Michele Simionato]

Alex Martelli <aleax at aleax.it> wrote in message news:<t%vYa.29160$an6.1020776 at news1.tin.it>...
> "__getattr__ is skipped" is false (the
> __getattr__ a *metaclass* could define would indeed be used as
> equivalent to the class defining methods) -- the _class_'s __getattr__
> if any is irrelevant because it's used on class *instances* (as
> the language reference also says a few pages later) and thus it's
> not the *CLASS* that's defining "methods with special names" here.
> 

Alex, did you look at the thread I mentioned? Here is the problem
with __getattr__ in metaclasses for special methods (quoting from
that thread).

"""
defining __len__ on the class does not work:

class M(type):
    def __getattr__(self,name):
            if name=='__len__': return lambda self:0

class F: __metaclass__=M

>>> f=F()
>>> F.__len__(f) # okay 0
>>> len(f) # TypeError: len() of unsized object
f.__len__() # AttributeError: 'F' object has no attribute '__len__'

As you see, the problem is that len(x) is not calling x.__len__(),
nor x.__class__.__len__(x); I really would like to know how ``len`` 
(or ``str``, ``repr``, etc.) work.
"""

If you remember, Bjorn Pettersen reported this (or something similar)
months ago. I am saying that this behaviour is not documented, at
least AFAIK.


             Michele