[Python-Dev] Alternative to more ABCs [was:] Iterable String Redux (aka String ABC) (original) (raw)

Raymond Hettinger python at rcn.com
Sun Jun 1 03:41:40 CEST 2008

From: "Guido van Rossum" <guido at python.org>

I'm willing to meet you halfway. I really don't want isinstance(x, str) to return True for something that doesn't inherit from the concrete str type; this is bound to lead to too much confusion and breakage.

Probably true. It was an attractive idea though. Unless all client code converts all its isinstance() tests from concrete to abstract, life is going to be tough for people writing look-alike classes which will have limited applicability.

But I'm fine with a String ABC (or any other ABC, e.g. Atomic?) that doesn't define any methods but can be used for type testing. How about that?

That's progress! It makes abstract substitution possible while still saving us a lot of code and avoiding over-specification.

I propose the following empty abstract classes:
String, Datetime, Deque, and Socket.

-1 on Atomic though. Earlier in the thread it was made clear that that atomicity is not an intrinsic property of a type; instead it varies across applications (when flattening email folders, a multi-part mime message is atomic, but when flattening individual messages, a multi-part mime message is just another nested container, part of the tree, not one of the leaves).

Are you open to considering numbers.Integral to be one of the new empty abstract classes? That would make it much easier for objects wanting to pass themselves as integers. As it stands now, an aspiring Integral class is required to implement a number of arcana including: rxor, rrshift, pow, invert, index, and long.

Raymond

More information about the Python-Dev mailing list