[Python-Dev] PEP 552: deterministic pycs

Antoine Pitrou solipsis at pitrou.net
Thu Sep 7 17:21:27 EDT 2017

On Thu, 07 Sep 2017 14:08:58 -0700
Benjamin Peterson <benjamin at 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 at 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.

Not sure how common that situation is (certainly the source tree wasn't
read-only when you checked it out or untar'ed it), but isn't it easily
circumvented by copying the source tree before building?

> This proposal also allows reproducible builds even if the files are
> being modified in an edit-run-tests cycle.

I don't follow you here.  Could you elaborate?



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