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spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:34716 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l7hTv-0003Tp-01 for qemu-devel@archiver.kernel.org; Thu, 04 Feb 2021 11:27:47 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:34550) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l7hNO-0005Sf-Qg for qemu-devel@nongnu.org; Thu, 04 Feb 2021 11:21:02 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:49934) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l7hNK-000454-Tq for qemu-devel@nongnu.org; Thu, 04 Feb 2021 11:21:01 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612455657; h=from:from: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=qK1/RCTsD0n/mkJWTAuC6fzy3GxAICPpud0x4USovmc=; b=jFUC7mUgcQ4JQ46zL8kR/8o9a1viI7LeeUe7itMozjG9nbbvTPQCUJuukHMhCRumez8qJX vkTr60yor2CZTKL3vhN0sbs+GrxPnm9L7HVwp2SQinI3qTZL2NWn1Zww3D4/k3WG0yRnQq CJ+LpksxH207NVnpep+OrBIZfZFkwD0= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-255--qM6dMNxNBODco3ki54EBA-1; Thu, 04 Feb 2021 11:20:51 -0500 X-MC-Unique: -qM6dMNxNBODco3ki54EBA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id CE6CE8030B3; Thu, 4 Feb 2021 16:20:49 +0000 (UTC) Received: from [10.10.112.247] (ovpn-112-247.rdu2.redhat.com [10.10.112.247]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3655D60BF1; Thu, 4 Feb 2021 16:20:49 +0000 (UTC) Subject: Re: [PATCH v4 08/14] qapi/introspect.py: create a typed 'Annotated' data strutcure To: Markus Armbruster , Eduardo Habkost References: <20210202174651.2274166-1-jsnow@redhat.com> <20210202174651.2274166-9-jsnow@redhat.com> <878s85tdh3.fsf@dusky.pond.sub.org> <20210203215026.GB126021@habkost.net> <87a6sjdet2.fsf@dusky.pond.sub.org> From: John Snow Message-ID: <77cc0262-3192-130f-81d8-a72193bf1020@redhat.com> Date: Thu, 4 Feb 2021 11:20:48 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <87a6sjdet2.fsf@dusky.pond.sub.org> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=jsnow@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=jsnow@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -32 X-Spam_score: -3.3 X-Spam_bar: --- X-Spam_report: (-3.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.351, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.182, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=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: Michael Roth , qemu-devel@nongnu.org, Cleber Rosa Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2/4/21 10:37 AM, Markus Armbruster wrote: > Eduardo Habkost writes: > >> On Wed, Feb 03, 2021 at 03:47:36PM +0100, Markus Armbruster wrote: >>> John Snow writes: >>> >>>> Presently, we use a tuple to attach a dict containing annotations >>>> (comments and compile-time conditionals) to a tree node. This is >>>> undesirable because dicts are difficult to strongly type; promoting it >>>> to a real class allows us to name the values and types of the >>>> annotations we are expecting. >>>> >>>> In terms of typing, the Annotated type serves as a generic container >>>> where the annotated node's type is preserved, allowing for greater >>>> specificity than we'd be able to provide without a generic. >>>> >>>> Signed-off-by: John Snow >> [...] >>>> +class Annotated(Generic[_NodeT]): >>>> + """ >>>> + Annotated generally contains a SchemaInfo-like type (as a dict), >>>> + But it also used to wrap comments/ifconds around scalar leaf values, >>>> + for the benefit of features and enums. >>>> + """ >>>> + # Remove after 3.7 adds @dataclass: >>> >>> Make this >>> >>> # TODO Remove after Python 3.7 ... >>> >>> to give us a fighting chance to remember. >>> >>>> + # pylint: disable=too-few-public-methods >>>> + def __init__(self, value: _NodeT, ifcond: Iterable[str], >>>> + comment: Optional[str] = None): >>> >>> Why not simply value: _value? >> >> Example: >> x = C(1) >> y: C[int] >> y = C('x') # mistake >> >> Declaring value as _NodeT does: >> - Make the inferred type of x be Annotated[int]. >> - Catch the mistake above. > > I smell overengineering. I may well be wrong. > > Without doubt, there are uses for using the type system for keeping > SomeGenericType[SomeType] and SomeGenericType[AnotherType] apart. > > But what do we gain by keeping the Annotated[T] for the possible T > apart? > > _tree_to_qlit() doesn't care: it peels off the wrapper holding ifcond > and comment, and recurses for the JSON so wrapped. Regardless of what > was wrapped, i.e. what kind of T we got. > > Heck, it works just fine even if you wrap your JSON multiple times. It > doesn't give a hoot whether that makes sense. Making sense is the > caller's business. > > So what does care? > > Or am I simply confused? > > > PS: As far as I can tell, _tree_to_qlit() doesn't give a hoot whether a > dictionary's values are wrapped, either. > You're right that it offers no necessary power to the automated checking, I cede as much in my other replies to you. (1) I hope the explanation was helpful, because the technique will return for structures like QAPISchemaMember where it does become more obviously useful to disambiguate the wrapped types. (2) It still has a notational benefit to the human for documentation and IDE purposes, e.g. at the end of this series: ``` self._trees: List[Annotated[SchemaInfo]] = [] ``` That's nice! It tells us exactly what's in there. Does it work if I dumb it down to just: ``` self.trees: List[AnnotatedThingy] = [] ``` Yes, but it's worse to the human and the IDE both. I consider type hints as serving a dual purpose; both provability and declaration of intent. --js