[Python-Dev] PEP 552: deterministic pycs

[Brett Cannon]

On Fri, 8 Sep 2017 at 10:53 Benjamin Peterson <benjamin at python.org> wrote:

> Thank you all for the feedback. I've now updated the PEP to specify a
> 4-word pyc header with a bit field in every case.
>
> On Fri, Sep 8, 2017, at 09:43, Nick Coghlan wrote:
> > On 8 September 2017 at 07:55, Antoine Pitrou <solipsis at pitrou.net>
> wrote:
> > > On Fri, 8 Sep 2017 07:49:46 -0700
> > > Nick Coghlan <ncoghlan at gmail.com> wrote:
> > >> > I'd rather a single magic number and a separate bitfield that tells
> > >> > what the header encodes exactly.  We don't *have* to fight for a
> tiny
> > >> > size reduction of pyc files.
> > >>
> > >> One of Benjamin's goals was for the existing timestamp-based pyc
> > >> format to remain completely unchanged, so we need some kind of marker
> > >> in the magic number to indicate whether the file is using the new
> > >> format or nor.
> > >
> > > I don't think that's a useful goal, as long as we bump the magic
> number.
> >
> > Yeah, we (me, Benjamin, Greg) discussed that here, and we agree -
> > there isn't actually any benefit to keeping the timestamp based pyc's
> > using the same layout, since the magic number is already going to
> > change anyway.
> >
> > Given that, I think your suggested 16 byte header layout would be a
> > good one: 4 byte magic number, 4 bytes reserved for format flags, 8
> > bytes with an interpretation that depends on the format flags.
> >
>

+1 from me!
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