[Python-Dev] PEP 552: deterministic pycs

Guido van Rossum guido at python.org
Thu Sep 7 17:43:16 EDT 2017

On Thu, Sep 7, 2017 at 2:40 PM, Benjamin Peterson <benjamin at python.org>

> 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.

> > 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.

--Guido van Rossum (python.org/~guido)
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