[Persistence-sig] "Straw Baby" Persistence API

[Steve Menard]

At 11:02 AM 7/22/2002 -0400, Jeremy Hylton wrote:
> >>>>> "SM" == Steve Menard <smenard@bigfoot.com> writes:
>
>   GvR> But perhaps these should be rewritten to derive from dict and
>   GvR> list instead of UserDict and UserList?
>   >>
>   >> One small comment.  (I owe more substantial comment on Phillip's
>   >> earlier proposals.)  The persistent versions of dict and list
>   >> can't extend the builtin types, because they need to hook
>   >> __getitem__() and __setitem__().  The overridden methods may not
>   >> be called if we extend the builtin types.
>   >>
>
>   SM> hum, if those method are not guaranteed to be called by
>   SM> subclassing dict or list, then there is something broken. Either
>   SM> that or there is a subtle thing I do not understand.
>
>The latter.  For performance reasons, most C code uses calls like
>PyDict_GetItem(), which operates directly on the C representation of a
>dict.  If you inherit from dict, you'll get the same C representation
>for your object.  That allows PyDict_GetItem() to be called, but
>doesn't arrange to call your __getitem__() method.  The indirection
>required to invoke a subclass's __getitem__() would cause serious
>performance problems.

Ok, makes sense. Since it is unsafe to override those methods, perhaps it 
should be disallowed then. Because we get different behavior when obj[x] is 
called from C and when called from Python.

>Normally Guido only recommends inheriting from dict to add new
>behavior (as opposed to customizing existing behavior).

         Steve