[Python-Dev] Data descriptor doc/implementation inconsistency (original) (raw)

Michael Foord fuzzyman at voidspace.org.uk
Mon Jan 11 23:11:44 CET 2010

On 11/01/2010 21:12, Nick Coghlan wrote:

Benjamin Peterson wrote: > My question is: Is this a doc bug or a implementation bug? If the

former, it will be the description of a data descriptor much less consistent, since it will require that a get method be present, too. If the latter, the fix may break some programs relying on the ability to "cache" a value in the instance dictionary.

[1] http://docs.python.org/reference/datamodel#invoking-descriptors [snip...] Note that the behaviour here is still different from that of a data descriptor: with a data descriptor, once it gets shadowed in the instance dictionary, the descriptor is ignored completely. The only way to get the descriptor involved again is to eliminate the shadowing. The non-data descriptor with only set is just choosing not to override the attribute lookup process.

Does that mean we need a third class of descriptors that are neither data descriptors nor non-data descriptors?

What should we call them: really-not-data-descriptors?

All the best,

Michael

Cheers, Nick.

-- http://www.ironpythoninaction.com/ http://www.voidspace.org.uk/blog

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