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dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:57080 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kMtrU-0001TX-0L for qemu-devel@archiver.kernel.org; Mon, 28 Sep 2020 10:10:40 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:47806) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kMtpr-0000Zi-FP for qemu-devel@nongnu.org; Mon, 28 Sep 2020 10:09:01 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:39873) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kMtpl-0001XU-Jp for qemu-devel@nongnu.org; Mon, 28 Sep 2020 10:08:58 -0400 Dkim-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1601302132; 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=GOhkvWRgj0ofZ/i5j9UKTGrIoSa/zfgmcFeF808iNrs=; b=P/pC5zPM9i3/ur8bCs1a8c0q+D+pYU5D8xr+tiryFKVww+CJyGutB4Kvsi7Y5qaUq85ioB 0z0HRSiQk0fZUgfVdKIUwEFtPfwFj2fZzLxtTy2bzy7HpNyxdTlpOKWRmThvto2ckbaAYr /DvpDxBYk50QaTiQo+uHFnQqdd1tKTI= 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-147-6792NafiM9aLzngzBN0BIA-1; Mon, 28 Sep 2020 10:08:48 -0400 X-MC-Unique: 6792NafiM9aLzngzBN0BIA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 26450807352; Mon, 28 Sep 2020 14:08:45 +0000 (UTC) Received: from [10.10.119.140] (ovpn-119-140.rdu2.redhat.com [10.10.119.140]) by smtp.corp.redhat.com (Postfix) with ESMTP id CDD885C1BB; Mon, 28 Sep 2020 14:08:43 +0000 (UTC) Subject: Re: [PATCH v2 28/38] qapi/gen.py: update write() to be more idiomatic To: Markus Armbruster , Eric Blake References: <20200922210101.4081073-1-jsnow@redhat.com> <20200922210101.4081073-29-jsnow@redhat.com> <20200923152624.GO3312949@habkost.net> <20200924155959.GC191229@localhost.localdomain> <87r1qqro8i.fsf@dusky.pond.sub.org> <20200925132458.GJ2178035@redhat.com> <874knmq7yg.fsf@dusky.pond.sub.org> <87y2kugl1z.fsf@dusky.pond.sub.org> From: John Snow Message-ID: Date: Mon, 28 Sep 2020 10:08:43 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <87y2kugl1z.fsf@dusky.pond.sub.org> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 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-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/28 03:29:35 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.687, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=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: Peter Maydell , =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= , Eduardo Habkost , qemu-devel@nongnu.org, Michael Roth , Cleber Rosa , =?UTF-8?Q?Alex_Benn=c3=a9e?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 9/28/20 8:09 AM, Markus Armbruster wrote: > Eric Blake writes: > >> On 9/25/20 8:52 AM, Markus Armbruster wrote: >> >>>>> This was my best attempt to open the file read/write, creating it if it >>>>> doesn't exist. >>>>> >>>>> Plain >>>>> >>>>> f = open(pathname, "r+", encoding='utf-8') >>>>> >>>>> fails instead of creates, and >>>>> >>>>> f = open(pathname, "w+", encoding='utf-8') >>>>> >>>>> truncates. >>>>> >>>>> If you know a better way, tell me! >>>> >>>> IIUC, you need "a+" as the mode, rather than "w+" >>> Sure this lets me do >>> f.seek(0) >>> f.truncate(0) >>> f.write(text) >>> to overwrite the old contents on all systems? >> >> As long as you do a single pass over the output (you issue a stream of >> f.write() after the truncate, but never a seek), then this will work. > > Well, I do seek(), right before the truncate. > >>> Documentation cautions: >>> [...] 'a' for appending (which on some Unix systems, means that >>> all >>> writes append to the end of the file regardless of the current seek >>> position). >> >> Yes, that means that random access is impossible on such a stream. >> But not all file creation patterns require random access. > > To be honest, I still prefer the code I wrote, because there the reader > only wonders why I didn't just open(), while here we get to argue about > subtleties of mode "a+". > I kept your os.open, I agree with you here. (I still rewrote to use the context managers, though.)