[Python-Dev] About 'superobject' and descriptors (original) (raw)

Steven D'Aprano steve at pearwood.info
Thu Oct 24 01:48:51 CEST 2013

Hi Hakril,

I think this question is probably off-topic for this list. This list is for development of the Python compiler, not for development with Python, and questions like this should probably go to python-list at python.org (also mirrored as comp.lang.python if you have Usenet access). But I have a brief observation below:

On Wed, Oct 23, 2013 at 07:29:03PM +0200, hakril lse wrote:

For example:

# A.descr is a descriptor # B inherit from A # C inherit from B c = C() c.descr super(C, c).descr super(B, c).descr In these 3 cases the get method is called with the same arguments that are : get(descr, c, C). If this behavior is really expected: Could you explain why ? because it means that I am missing something obvious. Because, at first sight, the 'type' argument seems to be the perfect place to get the type of the 'real calling class'.

I'm afraid I don't understand what you mean by "real calling class", if it is not the class of the instance doing the calling.

I have a feeling that perhaps you think that calls to super are equivalent to "the parent of the class", and so you expect:

c.desc => desc.get(c, C) super(C, c).desc => desc.get(c, B) super(B, c).desc => desc.get(c, A)

but that would not be correct. super is equivalent to "the next class in the MRO of the instance doing the calling", and in all cases, the "real-calling instance" is c, and the "real calling class" is the class of c, namely C.

Extended discussion of this should go to python-list, but I think I have the basics right.

-- Steven

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