[Python-Dev] Patch to use dict subclasses in eval(), exec (original) (raw)

Guido van Rossum guido@python.org
Tue, 29 Oct 2002 14:26:26 -0500

>Correct. I don't see this as a huge limitation -- all "autoload" >features that I'm familiar with (Emacs, Tcl; how about Perl?) require >you to know at least the auto-loaded names in advance. (Also in my >defence you only mentioned the cost of unpickling everything as an >argument. :-)

Perl doesn't require it. If a method call is made but that method name doesn't appear in the object's inheritance hierarchy, perl walks up the tree looking for a method named AUTOLOAD and if it finds one calls that. The AUTOLOAD method then has the opportunity to do something--satisfy the call, dispatch to a parent class, or pitch a fit. It's valid for an AUTOLOAD method to satisfy the request without instantiating a method for it. (In which case the next invocation of that method will end up back in AUTOLOAD)

Um, as long we're doing method lookup, Python's getattr can do all that.

Works for subroutines too, though the hierarchy isn't supposed to be walked for those. (Older versions of perl would do it, but that's been deprecated)

OK, so if there's a global AUTOLOAD and no global x, looking for x will call AUTOLOAD to satisfy x, right? Python doesn't do this, and this is what the "hookable namespace" feature is aiming at.

--Guido van Rossum (home page: http://www.python.org/~guido/)