[Python-Dev] Python-versus-CPython question for __mul__ dispatch

Nathaniel Smith njs at pobox.com
Fri May 15 23:35:38 CEST 2015

On Thu, May 14, 2015 at 11:53 PM, Nathaniel Smith <njs at pobox.com> wrote:
> On Thu, May 14, 2015 at 9:29 PM, Guido van Rossum <guido at python.org> wrote:
>> I expect you can make something that behaves like list by defining __mul__
>> and __rmul__ and returning NotImplemented.
> Hmm, it's fairly tricky, and part of the trick is that you can never
> return NotImplemented (because you have to pretty much take over and
> entirely replace the normal dispatch rules inside __mul__ and
> __rmul__), but see attached for something I think should work.
> So I guess this is just how Python's list, tuple, etc. work, and PyPy
> and friends need to match...

For the record, it looks like PyPy does already have a hack to
implement this -- they do it by having a hidden flag on the built-in
sequence types which the implementations of '*' and '+' check for, and
if it's found it triggers a different rule for dispatching to the
__op__ methods:

Nathaniel J. Smith -- http://vorpus.org

More information about the Python-Dev mailing list