> The main objection to that model is that it requires modifying source
timestamps, which isn't possible for builds on read-only source trees.

Why not set the source timestamps of the source trees to say 1 first? That's what is done with the Nix package manager. The Python interpreter is patched (mostly similar to the referred PR) and checks whether SOURCE_DATE_EPOCH is set, and if so, sets the mtime to 1.

On Thu, Sep 7, 2017 at 11:08 PM, Benjamin Peterson <benjamin@python.org> wrote:


On Thu, Sep 7, 2017, at 14:00, Antoine Pitrou wrote:
> On Thu, 07 Sep 2017 13:39:21 -0700
> Benjamin Peterson <benjamin@python.org> wrote:
> > Hello,
> > I've written a short PEP about an import extension to allow pycs to be
> > more deterministic by optional replacing the timestamp with a hash of
> > the source file: https://www.python.org/dev/peps/pep-0552/
>
> Why isn't https://github.com/python/cpython/pull/296 a good enough
> solution to this problem?  It has a simple implementation, and requires
> neither maintaining two different pyc formats nor reading the entire
> source file to check whether the pyc file is up to date.

The main objection to that model is that it requires modifying source
timestamps, which isn't possible for builds on read-only source trees.
This proposal also allows reproducible builds even if the files are
being modified in an edit-run-tests cycle.
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