[Python-Dev] PEP 552: deterministic pycs

[Nick Coghlan]

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.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia