[Python-Dev] PEP 552: deterministic pycs (original) (raw)

Nick Coghlan ncoghlan at gmail.com
Fri Sep 8 12:43:54 EDT 2017

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

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