[Python-Dev] Clarification on MRO when inheriting from builtin type.

[Paul Sokolovsky]

Hello,

On Mon, 28 Apr 2014 13:13:53 +1000
Chris Angelico <rosuav at gmail.com> wrote:

> On Mon, Apr 28, 2014 at 12:59 PM, Paul Sokolovsky <pmiscml at gmail.com>
> wrote:
> > From the output, "User" class as expected does not override
> > list.append(), but does override list.__str__(). Is this behavior
> > documented somewhere (complete arrangement)? What's the rationale
> > behind it?
> 
> In Python 3.4 (don't know about other versions), list.__str__ doesn't
> exist; when you call str([1,2,3]) it calls object.__str__. The MRO for
> C is (C, list, User, object) so anything from list (eg append) takes
> precedence over anything from User, but anything list doesn't have
> will fall through to User before catching object.

Thanks for quick response! I see that list.__repr__ exists, and test
using it works "as expected". Hopefully, such stuff can be treated as
implementation-specific details...

> 
> ChrisA

-- 
Best regards,
 Paul                          mailto:pmiscml at gmail.com