[ZODB-Dev] Persistent-derived class instances always callable

[Shane Hathaway]

John Belmonte wrote:
> With python 2.3.2 and ZODB 3.2c1:
> 
>   >>> import ZODB
>   >>> from Persistence import Persistent
>   >>> class Foo(Persistent): pass
>   >>> a = Foo()
>   >>> callable(a)
>   True
> 
> What's going on here?

ExtensionClass.Base, a C type, fills the tp_call slot.  callable() looks 
to see if tp_call is non-null and considers this check to be 
authoritative.  Although some ExtensionClass instances are callable and 
some are not, callable() doesn't go to the effort of discerning the 
difference, so it always returns True for ExtensionClass instances.

I think that callable() should only return True if the object has a 
__call__ attribute.  Now that even functions and methods have __call__ 
attributes (Python 2.2+), simply checking for the presence of __call__ 
is actually more reliable than the current callable() implementation.

Shane