[Python-Dev] About [].append == [].append (original) (raw)

Nathaniel Smith njs at pobox.com
Thu Jun 21 17:59:19 EDT 2018

On Thu, Jun 21, 2018 at 2:04 PM, Ivan Pozdeev via Python-Dev <python-dev at python.org> wrote:

On 21.06.2018 23:40, Guido van Rossum wrote:

> I'm with Serhiy here, for mutable values I don't think the methods should > compare equal, even when the values do. For immutables I don't care either > way, it's an implementation detail. In this light, methods rather shouldn't have a rich comparison logic at all -- at the very least, until we have a realistic use case and can flesh out the requirements for it.

== and hashing for methods can be quite useful for things like cache keys. (E.g., a dict mapping callable+args -> result.) I'm sure people are using it. So I think simply removing it would be pretty disruptive.

I can't think of any cases where == and hashing are useful for methods on mutable objects, which is that case where it matters whether the 'self' comparison uses == or 'is', but the method object doesn't know whether 'self' is mutable, so it has to either work in general or not work in general.

-n

-- Nathaniel J. Smith -- https://vorpus.org

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