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Tue, 8 Jun 2021 15:57:59 +0200 (CEST) From: Markus Armbruster To: John Snow Subject: Re: [PATCH v3 3/9] qapi: start building an 'if' predicate tree References: <20210429134032.1125111-1-marcandre.lureau@redhat.com> <20210429134032.1125111-4-marcandre.lureau@redhat.com> <5d0a776e-e597-6996-c407-cd2d91883eac@redhat.com> <87eee02ldl.fsf@dusky.pond.sub.org> <12434341-9054-8c35-e8a4-59087548b59e@redhat.com> Date: Tue, 08 Jun 2021 15:57:59 +0200 In-Reply-To: <12434341-9054-8c35-e8a4-59087548b59e@redhat.com> (John Snow's message of "Fri, 21 May 2021 12:18:03 -0400") Message-ID: <87v96oxxug.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=216.205.24.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.197, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: marcandre.lureau@redhat.com, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" John Snow writes: > On 5/21/21 10:48 AM, Markus Armbruster wrote: >> Beware, I'm skimming, not really reviewing. >>=20 >> John Snow writes: >>=20 >>> On 4/29/21 9:40 AM, marcandre.lureau@redhat.com wrote: [...] >>>> index b7f475a160..59a7ee2f32 100644 >>>> --- a/scripts/qapi/common.py >>>> +++ b/scripts/qapi/common.py >>>> @@ -11,8 +11,9 @@ >>>> # This work is licensed under the terms of the GNU GPL, version 2. >>>> # See the COPYING file in the top-level directory. >>>> +from abc import ABC, abstractmethod >>>> import re >>>> -from typing import Optional >>>> +from typing import Optional, Sequence >>>> =20 >>>> #: Magic string that gets removed along with all space to its right= . >>>> @@ -192,3 +193,54 @@ def guardend(name: str) -> str: >>>> #endif /* %(name)s */ >>>> ''', >>>> name=3Dc_fname(name).upper()) >>>> + >>>> + >>>> +class IfPredicate(ABC): >>>> + @abstractmethod >>>> + def cgen(self) -> str: >>> >>> Like the review to patch 2, I'm not sure we want to bake cgen stuff >>> directly into this class. Are you going to have cgen() and rustgen() >>> methods all here? >>> >>>> + pass >>>> + >>> >>> I think you want raise NotImplementedError to specify a function that >>> the inheriting class MUST implement. Otherwise, there's little value >>> to allow a child class to call super() on a method that doesn't have a >>> default implementation. >>> >>> You *could* drop the (ABC) and the @abstractmethod decorators if you do= so. >>> >>> Matters of taste and style. >>=20 >> We're not coding a library for use by thousands of people. If we did, >> then complicating the code to guard against misuse could be a win. But >> we don't. >>=20 >> schema.py is full of methods that pass. Maybe some of them need to be >> overriden by any conceivable subtype. Who cares? The subtypes either >> work or they don't. I prefer >>=20 >> def frobnicate: >> pass >>=20 >> to >>=20 >> def frobnicate: >> raise NotImplementedError >>=20 >> One, pass is easier on the eyes. Two, a subtype's .frobnicate() can >> blindly call super().frobnicate(). >>=20 > > "pass" here operates as a syntactic sugar for "return None" which has=20 > implications on the return type. It's short, but wrong. Nitpicking... pass is not specified as syntactic sugar: 7.4. The pass statement pass_stmt ::=3D "pass" pass is a null operation =E2=80=94 when it is executed, nothing happens= . It is useful as a placeholder when a statement is required syntactically,= but no code needs to be executed, for example: def f(arg): pass # a function that does nothing (yet) class C: pass # a class with no methods (yet) What really happens in def foo(): pass is what *always* happens when control reaches the end of the function body: the function returns None. Further evidence: >>> def baz(): ... pass ... return 42 ...=20 >>> baz() 42 > raise NotImplementedError means something different semantically. > > To me, pass is *NOT* easier on the eyes, it is misleading. It is=20 > idiomatic to use NotImplementedError if it is not acceptable for a=20 > default implementation to return None. > > I understand perfectly well the desire to keep things simple, but what=20 > is actually "simple" depends on the expectations of the programmer. I=20 > err towards idiomatic Python. What's your take on "Two, a subtype's .frobnicate() can blindly call super().frobnicate()"? [...]