Getting a class name

[Fuzzyman]

On Feb 18, 1:22 pm, "Michele Simionato" <michele.simion... at gmail.com>
wrote:
> On Feb 18, 1:24 pm, "Fuzzyman" <fuzzy... at gmail.com> wrote:
>
> > Why is the __name__ attribute not available to the instance? Why don't
> > normal lookup rules apply (meaning that a magic attribute will be
> > looked up on the class for instances) ?
>
> Because __name__ isn't really an attribute, it is a descriptor defined
> on
> the metaclass:
>
> >>> type(type.__dict__['__name__'])
>
> <type 'getset_descriptor'>
>
> Seehttp://users.rcn.com/python/download/Descriptor.htmfor a guide to
> descriptors, and the papers by me and David Mertz for a guide to
> metaclasses.
>

Thanks, I'll do some more reading.

I got as far as this on my own:

My guess is that it is because magic attributes are looked up on the
class. When you ask the *class* what its name is, the metaclass
answers on its behalf.

The class has no real ``__name__`` attribute, so when you ask the
instance (which doesn't inherit from the metaclass) you get an
``AttributeError``. Is this right ? In which case, how does the
metaclass (typically ``type`` which has many instance) know which
answer to supply ?

A simple test indicates that the name *is* looked up on the
metaclass :

.. raw:: html

    {+coloring}
    >>> class meta(type):
    ...     __name__ = 'fish'
    ...
    >>> class Test(object):
    ...     __metaclass__ = meta
    ...
    >>> Test.__name__
    'fish'
    {-coloring}

So maybe ``__name__`` is a propery and ``type`` keeps a dictionary of
instances to names, registered in ``type.__new__`` ?

Fuzzyman
http://www.voidspace.org.uk/python/articles.shtml

>  Michele Simionato