Re: [PATCH v2 28/38] qapi/gen.py: update write() to be more idiomatic

[Markus Armbruster]

Cleber Rosa <crosa@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 <jsnow@redhat.com>
>> > 
>> > Reviewed-by: Eduardo Habkost <ehabkost@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!