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 X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5D9CEC4363D for ; Fri, 25 Sep 2020 16:08:18 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id E0AC1235FD for ; Fri, 25 Sep 2020 16:08:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="iwSwhVXK" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E0AC1235FD Authentication-Results: mail.kernel.org; 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]:50822 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kLqGe-00057U-W0 for qemu-devel@archiver.kernel.org; Fri, 25 Sep 2020 12:08:17 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:37766) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kLpwl-00017H-MG for qemu-devel@nongnu.org; Fri, 25 Sep 2020 11:47:44 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:23808) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kLpwb-0000EM-U3 for qemu-devel@nongnu.org; Fri, 25 Sep 2020 11:47:42 -0400 Dkim-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1601048850; 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=qBMGmx+o2S9GK6JncI/rK6bcegbvSjtxVQoXApwVBPA=; b=iwSwhVXKVLDh1muep4ofNuxzXUZZM4kQ490IOCMIv5CFcV56BztG3M8un5H9Jx3yVGRM9A ZZ9LRb3z9MFPZvN3/a1inQ4N7xljE6NT7fdN6CQsfsnj8fPrYDfUQNqBFnEtF/lWKPutwg tmuyLMWz0Dg7qVM+hconVDHyUX5NDKA= 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-337-snbg52eJNeeDBpJq8VVEJg-1; Fri, 25 Sep 2020 11:47:24 -0400 X-MC-Unique: snbg52eJNeeDBpJq8VVEJg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A450218A2252; Fri, 25 Sep 2020 15:47:19 +0000 (UTC) Received: from [10.3.114.148] (ovpn-114-148.phx2.redhat.com [10.3.114.148]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E697573692; Fri, 25 Sep 2020 15:47:18 +0000 (UTC) Subject: Re: [PATCH v2 28/38] qapi/gen.py: update write() to be more idiomatic To: Markus Armbruster , =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= 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> From: Eric Blake Organization: Red Hat, Inc. Message-ID: Date: Fri, 25 Sep 2020 10:47:18 -0500 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: <874knmq7yg.fsf@dusky.pond.sub.org> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eblake@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=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/25 02:48:20 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.199, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.238, 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 , Eduardo Habkost , =?UTF-8?Q?Alex_Benn=c3=a9e?= , Michael Roth , qemu-devel@nongnu.org, Cleber Rosa , John Snow Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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. > > 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. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org