[Python-3000] Need help completing ABC pep (original) (raw)

John Reese jtr at miskatonic.nu
Sat Apr 21 22:21:26 CEST 2007

On 4/19/07, Guido van Rossum <guido at python.org> wrote:

I've started a PEP on Abstract Base Classes (ABCs), PEP 3119:

http://www.python.org/dev/peps/pep-3119/ While I'm not ready yet to answer tough questions about this compared to alternative proposals, I am ready for feedback on the various open issues sprinkled throughout the current text, especially concerning decisions regarding exactly which operations to include in the various ABCs, and also regarding the level of detail required in the PEP. -- --Guido van Rossum (home page: http://www.python.org/~guido/)

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"This PEP proposes a particular strategy for organizing these tests known as Abstract Base Classes, or ABC. ABCs are simply Python classes that are added into an object's inheritance tree to signal certain features of that object to an external inspector. Tests are done using isinstance(), and the presence of a particular ABC means that the test has passed."

I'd like to see another few lines in the rationale section explaining the intent of the concrete methods. For example, inheriting from abc.Mapping would have a similar effect to inheriting from UserDict.DictMixin -- by overriding it's few abstract methods you get close to the full complement of dict's convenience methods. But from the open issues and other discussion in this thread, I don't think the intention is to provide full coverage of the convenience methods in all of the builtin classes in their corresponding ABCs, but merely to expand the number of methods you can assume given an ABC.

I'd like an explanation of exactly where the line is being drawn in terms of what convenience methods ABCs will provide through concrete methods.

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