[Python-Dev] PEP 318 (was re: redefining is)

[David Eppstein]

In article <20040323224817.E8BD.JCARLSON at uci.edu>,
 Josiah Carlson <jcarlson at uci.edu> wrote:

> > perhaps two distinct objects.  How can one determine straightforwardly
> > whether those objects are members of the same equivalence class?
> 
> You were there and helped point out some of the limitations of the
> original code I posted, which now has a _straightforward_ recursive
> implementation here:
> http://mail.python.org/pipermail/python-dev/2004-March/043357.html

Heh, another use for the class variant of PEP 318.  Josiah's code 
depends on knowing which classes have immutable instances, using a 
hardcoded set of builtin types.  With PEP318, one could do

class foo [immutable]:
    ...

with an appropriate definition of immutable that either decorates the 
class object or adds to the set of known immutables.  Perhaps also with 
code to catch and warn against obvious attempts at mutation of foos...

-- 
David Eppstein                      http://www.ics.uci.edu/~eppstein/
Univ. of California, Irvine, School of Information & Computer Science