Daniel P. Berrangé <berra...@redhat.com> writes:
> On Fri, Sep 25, 2020 at 03:15:57PM +0200, Markus Armbruster wrote:
>> Cleber Rosa <cr...@redhat.com> writes:
>>
>> > 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.)
>> >> > >
>> >> > > Use exist_ok=True 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.
>> >> > >
>> >> > > Signed-off-by: John Snow <js...@redhat.com>
>> >> >
>> >> > Reviewed-by: Eduardo Habkost <ehabk...@redhat.com>
>> >> >
>> >> > I really miss a comment below explaining why we use
>> >> > open(os.open(pathname, ...), ...) instead of open(pathname, ...).
>>
>> This code:
>>
>> fd = os.open(pathname, os.O_RDWR | os.O_CREAT, 0o666)
>> f = open(fd, 'r+', encoding='utf-8')
>>
>> >> 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?
>> >>
>> >> 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.
>>
>> 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?
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).
