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Fri, 25 Sep 2020 15:52:55 +0200 (CEST) From: Markus Armbruster To: Daniel P. =?utf-8?Q?Berrang=C3=A9?= Subject: Re: [PATCH v2 28/38] qapi/gen.py: update write() to be more idiomatic 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> Date: Fri, 25 Sep 2020 15:52:55 +0200 In-Reply-To: <20200925132458.GJ2178035@redhat.com> ("Daniel P. =?utf-8?Q?B?= =?utf-8?Q?errang=C3=A9=22's?= message of "Fri, 25 Sep 2020 14:24:58 +0100") Message-ID: <874knmq7yg.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 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=63.128.21.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/25 01:07:33 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] 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=-1.199, 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_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 , John Snow , qemu-devel@nongnu.org, Michael Roth , Cleber Rosa , Alex =?utf-8?Q?Benn=C3=A9e?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Daniel P. Berrang=C3=A9 writes: > On Fri, Sep 25, 2020 at 03:15:57PM +0200, Markus Armbruster wrote: >> Cleber Rosa writes: >>=20 >> > On Wed, Sep 23, 2020 at 02:37:27PM -0400, John Snow wrote: >> >> On 9/23/20 11:26 AM, Eduardo Habkost wrote: >> >> > On Tue, Sep 22, 2020 at 05:00:51PM -0400, John Snow wrote: >> >> > > Make the file handling here just a tiny bit more idiomatic. >> >> > > (I realize this is heavily subjective.) >> >> > >=20 >> >> > > Use exist_ok=3DTrue for os.makedirs and remove the exception, >> >> > > use fdopen() to wrap the file descriptor in a File-like object, >> >> > > and use a context manager for managing the file pointer. >> >> > >=20 >> >> > > Signed-off-by: John Snow >> >> >=20 >> >> > Reviewed-by: Eduardo Habkost >> >> >=20 >> >> > I really miss a comment below explaining why we use >> >> > open(os.open(pathname, ...), ...) instead of open(pathname, ...). >>=20 >> This code: >>=20 >> fd =3D os.open(pathname, os.O_RDWR | os.O_CREAT, 0o666) >> f =3D open(fd, 'r+', encoding=3D'utf-8') >>=20 >> >> Not known to me. It was introduced in 907b846653 as part of an effort= to >> >> reduce rebuild times. Maybe this avoids a modification time change if= the >> >> file already exists? >> >>=20 >> >> Markus? >> > >> > AFACIT the change on 907b846653 is effective because of the "is new >> > text different from old text?" conditional. I can not see how the >> > separate/duplicate open/fdopen would contribute to that. >> > >> > But, let's hear from Markus. >>=20 >> This was my best attempt to open the file read/write, creating it if it >> doesn't exist. >>=20 >> Plain >>=20 >> f =3D open(pathname, "r+", encoding=3D'utf-8') >>=20 >> fails instead of creates, and >>=20 >> f =3D open(pathname, "w+", encoding=3D'utf-8') >>=20 >> truncates. >>=20 >> 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? 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).