From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 68594C61D9B for ; Wed, 22 Nov 2023 09:55:18 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1r5jwV-0005J1-Ns; Wed, 22 Nov 2023 04:54:47 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1r5jwS-0005Ih-QS for qemu-devel@nongnu.org; Wed, 22 Nov 2023 04:54:44 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1r5jwQ-00032B-Tt for qemu-devel@nongnu.org; Wed, 22 Nov 2023 04:54:44 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1700646882; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=hp5UNUcsY4uq9oMdemx/CvOpi4HVvsM0qvUGHm7ioIg=; b=W/p2rAtXCdcmliQrE57jL88UDJTluUMMzyEnLHOpWxrWuNoyJ/bPPGDygEt4Cp//VfFkZG Ueslxwy1SZLtqT3/+fu16CxvufHEqN/OnCgDjU2g77l511kR8cr62OKHzXT+SLzshmW7nU WuSZuRKH8UnQJ2Ichutl7a5rt/LM/s4= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-613-_2sHCGuPPb-zJQivSuohLg-1; Wed, 22 Nov 2023 04:54:38 -0500 X-MC-Unique: _2sHCGuPPb-zJQivSuohLg-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 4D90F3810B1C; Wed, 22 Nov 2023 09:54:38 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.104]) by smtp.corp.redhat.com (Postfix) with ESMTPS id F16831C060AE; Wed, 22 Nov 2023 09:54:36 +0000 (UTC) Date: Wed, 22 Nov 2023 09:54:34 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Markus Armbruster Cc: John Snow , qemu-devel , Peter Maydell , Michael Roth Subject: Re: [PATCH 05/19] qapi/schema: make c_type() and json_type() abstract methods Message-ID: References: <20231116014350.653792-1-jsnow@redhat.com> <20231116014350.653792-6-jsnow@redhat.com> <87jzqb4495.fsf@pond.sub.org> <87il5uw1zc.fsf@pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <87il5uw1zc.fsf@pond.sub.org> User-Agent: Mutt/2.2.10 (2023-03-25) X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.7 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Nov 22, 2023 at 10:50:47AM +0100, Markus Armbruster wrote: > Daniel P. Berrangé writes: > > > On Tue, Nov 21, 2023 at 11:28:17AM -0500, John Snow wrote: > >> On Tue, Nov 21, 2023, 8:43 AM Daniel P. Berrangé > >> wrote: > >> > >> > On Tue, Nov 21, 2023 at 02:36:54PM +0100, Markus Armbruster wrote: > >> > > John Snow writes: > >> > > > >> > > > These methods should always return a str, it's only the default > >> > abstract > >> > > > implementation that doesn't. They can be marked "abstract" by raising > >> > > > NotImplementedError(), which requires subclasses to override the method > >> > > > with the proper return type. > >> > > > > >> > > > Signed-off-by: John Snow > >> > > > --- > >> > > > scripts/qapi/schema.py | 8 ++++---- > >> > > > 1 file changed, 4 insertions(+), 4 deletions(-) > >> > > > > >> > > > diff --git a/scripts/qapi/schema.py b/scripts/qapi/schema.py > >> > > > index c5fdd625452..4600a566005 100644 > >> > > > --- a/scripts/qapi/schema.py > >> > > > +++ b/scripts/qapi/schema.py > >> > > > @@ -233,8 +233,8 @@ def visit(self, visitor): > >> > > > class QAPISchemaType(QAPISchemaEntity): > >> > > > # Return the C type for common use. > >> > > > # For the types we commonly box, this is a pointer type. > >> > > > - def c_type(self): > >> > > > - pass > >> > > > + def c_type(self) -> str: > >> > > > + raise NotImplementedError() > >> > > > > >> > > > # Return the C type to be used in a parameter list. > >> > > > def c_param_type(self): > >> > > > @@ -244,8 +244,8 @@ def c_param_type(self): > >> > > > def c_unboxed_type(self): > >> > > > return self.c_type() > >> > > > > >> > > > - def json_type(self): > >> > > > - pass > >> > > > + def json_type(self) -> str: > >> > > > + raise NotImplementedError() > >> > > > > >> > > > def alternate_qtype(self): > >> > > > json2qtype = { > >> > > > >> > > I wish abstract methods could be done in a more concise way. > >> > > >> > The canonical way would be to use the 'abc' module: > >> > > >> > from abc import ABCMeta, abstractmethod > >> > > >> > class A(metaclass=ABCMeta): > >> > @abstractmethod > >> > def foo(self): pass > >> > > >> > Not sure if the @abstractmethod decorator is enough to keep the static > >> > typing checker happy about a 'str' return type, when there is no body > >> > impl > >> > >> In practice, I'm under the belief that mypy and pylint both recognize a > >> method raising NotImplementedError as marking an abstract method without > >> needing to explicitly inherit from the ABC. > >> > >> I suppose there's also > >> https://docs.python.org/3/library/abc.html#abc.abstractmethod which I am > >> guessing just does this same thing. I'll see what makes mypy happy. I'm > >> assuming Markus would like to see something like this decorator to make it > >> more obvious that it's an abstract method. > > > > The 'abc' module described is an official PEP standard > > > > https://peps.python.org/pep-3119/ > > Compare: > > @abstractmethod > def c_type(self) -> str: > pass > > def c_type(self) -> str: > raise NotImplementedError() > > I prefer the former, because it's more explicit. > > Bonus: prevents accidental instantiation, and sub-classes don't need to > know what's abstract in the super-class, they can blindly use super() > calls. Being able to blindly call the parent impl via super() is more than just a bonus, it is a super compelling reason to use this. It protects your code against bugs from future re-factoring of the class hierarchy whether adding or removing parents. Even if we don't expect to need it for this particular class, I think this justifies having a policy of using 'abc' everywhere we need abstract methods. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|