[Python-Dev] PEP 552: deterministic pycs

[Benjamin Peterson]

On Thu, Sep 7, 2017, at 14:43, Guido van Rossum wrote:
> On Thu, Sep 7, 2017 at 2:40 PM, Benjamin Peterson <benjamin at python.org>
> wrote:
> 
> >
> >
> > On Thu, Sep 7, 2017, at 14:19, Guido van Rossum wrote:
> > > Nice one.
> > >
> > > It would be nice to specify the various APIs needed as well.
> >
> > The compileall and py_compile ones?
> >
> 
> Yes, and the SipHash mod to specify the key you mentioned.

Done.

> 
> >
> > > Why do you keep the mtime-based format as an option? (Maybe because it's
> > > faster? Did you measure it?)
> >
> > I haven't actually measured anything, but stating a file will definitely
> > be faster than reading it completely and hashing it. I suppose if the
> > speed difference between timestamp-based and hash-based pycs turned out
> > to be small we could feel good about dropping the timestamp format
> > completely. However, that difference might be hard to determine
> > definitely as I expect the speed hit will vary widely based on system
> > parameters such as disk speed and page cache size.
> >
> > My goal in this PEP was to preserve the current pyc invalidation
> > behavior, which works well today for many use cases, as the default. The
> > hash-based pycs are reserved for distribution and other power use cases.
> >
> 
> OK, maybe you can clarify that a bit in the PEP.

I've added a paragraph to the Rationale section.