A Suggestion (please read and respond)

[D-Man]

I seem to be missing something here:
	namely the message that this is a reply to.

Anyone know why I'm getting some, but not all messages?

-D


On Mon, 30 Oct 2000 15:35:31 Alex Martelli wrote:
> "Courageous" <jkraska1 at san.rr.com> wrote in message
> news:39FDAE7D.2259B2EC at san.rr.com...
>     [snip]
> > strict class Joe:
> >     i = 3
> > j = Joe()
> > j.j = 1
> >
> > >>>> Attribute error: strict classes only support instance attributes
> >      which also exist as class attributes. Valid instance attributes are:
> > 'i' (which is an integer in its class context)
> >
> > You could do something similar with every possible namespace, although
> > I haven't thought out what the syntax might be for modules...
> >
> > Note for classes you can, by overriding the set attr method, implement
> > this now.
> 
> Very, very true.  Moreover, you can do it by mix-in inheritance
> if you don't need to have your own special meaning for
> __setattr__ (if you do, you will need explicit delegation).
> 
> For example, this gets close:
> 
> -- cut: strict.py
> class Strict:
>     def __setattr__(self, name, value):
>         if hasattr(self.__class__,name):
>             self.__dict__[name]=value
>         else:
>             names = [x for x in self.__class__.__dict__.keys()
>                      if not x.startswith('__')]
>             names.sort()
>             message = ("Class %s is strict: only attributes %s can be set" %
>                 (self.__class__.__name__, names))
>             raise AttributeError,message
> -- end of cut
> 
> >>> import strict
> >>> class Mine(strict.Strict):
>             a=1; b=2; c="foo"; d=()
> 
>  >>> x=Mine()
> >>> x.a=23
> >>> x.z='foo'
> Traceback (innermost last):
>   File "<pyshell#20>", line 1, in ?
>     x.z='foo'
>   File "D:\Python20\strict.py", line 11, in __setattr__
>     raise AttributeError,message
> AttributeError: Class Mine is strict: only attributes ['a', 'b', 'c', 'd']
> can be set
> 
> However, the message is misleading for _inherited_ attributes (a bit too
> strict, let's say...):
> 
> >>> class Yours(Mine):
>  z=45; y='wep'
> 
> 
> >>> y=Yours()
> >>> y.z='plop'
> >>> y.a=23
> >>> y.n=42
> Traceback (innermost last):
>   File "<pyshell#48>", line 1, in ?
>     y.n=42
>   File "D:\Python20\strict.py", line 11, in __setattr__
>     raise AttributeError,message
> AttributeError: Class Yours is strict: only attributes ['y', 'z'] can be set
> >>>
> 
> It's not true -- attribute a can be set as well, as we have just
> demonstrated! -- but it ain't too hard to fix... left as an
> exercise to the reader!-)  [these metaprogramming tricks
> are fascinating, though I think their status is close to what
> Zen thinks of metaphysical reflections -- just a mind-
> obstacle in the quest for true simplicity...:-)]
> 
> 
> Alex
> 
> Thinking up strategies for that to be arranged gets
> interesting -- looking up a name in the graph of
> base classes each time, recursively, is not too hard
> of course:
> 
> def isnameok_inclass(klass, name):
>     if klass.__dict__.has_key(name):
>         return klass
>     for super in klass.__bases__:
>         isokthere=isnameok_inclass(super,name)
>         if isokthere: return isokthere
>     return None
> 
> def isnameok(object, name):
>     return isnameok_inclass(object.__class__, name)
> 
> and change the line in class Strict
>         if self.__class__.__dict__.has_key(name):
> into
>         if isnameok(self, name):
> 
> but optimizing that is more interesting.  For
> example, if we can assume that a class's bases
> are not changed during runtime (or if special
> re-processing can be required if they do), we
> could compute an '_allbases' field in a class
> the first time is needed:
> 
> def allbasesof(klass):
>     if not klass.__dict__.has_key('_allbases'):
>         all = list(klass.__bases__)
>         for super in klass.__bases__:
>             all.extend(allbasesof(super))
>         klass._allbases = all
>     return klass._allbases
> 
> 
> 
> 
> -- 
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>