[Python-ideas] PEP 526: why ClassVar instead of ClassAttr?

Guido van Rossum guido at python.org
Tue May 16 22:10:03 EDT 2017

It's "class variable" because we (at least I) also routinely use "instance

On Tue, May 16, 2017 at 4:23 PM, Steven D'Aprano <steve at pearwood.info>

> Since PEP 526 is already provisionally accepted, it may be too late to
> bring this up, but I have a question and suggestion about the name
> ClassVar. I've read the PEP but didn't see an answer or rejection to
> this.
> https://www.python.org/dev/peps/pep-0526/
> Why choose ClassVar over ClassAttr when the usual terminology used in
> the Python community is class and instance *attributes* rather than
> "variables"?
> I understand that, in a sense, attributes are variables (unless they're
> constants *wink*) but the term "class variable" sounds very Java-esque
> rather than Pythonic. And it is an uncomfortable fit with a language
> like Python where classes are first class values like ints, strings,
> floats etc:
> - we talk about a string variable meaning a variable holding a string;
> - a float variable is a variable holding a float;
> - a list variable is a variable holding a list;
> - so a class variable ought to be a variable holding a class.
> I get the intention: we have local, global, instance and class
> variables. But I feel that grouping instance/class with local/global is
> too abstract and "computer sciencey": in practice, instance/class vars
> are used in ways which are different enough from global/local vars that
> they deserve a different name: attributes, members or properties are
> common choices.
> (Python of course uses attributes, and properties for a particular kind
> of computed attribute.)
> This introduces split terminology: we now talk about annotating class
> attributes with ClassVar. Since there's no GlobalVar, NonLocalVar or
> LocalVar, there doesn't seem to be any good reason to stick with the
> FooVar naming system.
> Can we change the annotation to ClassAttr instead?
> --
> Steve
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--Guido van Rossum (python.org/~guido)
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