[Python-Dev] PEP 552: deterministic pycs

[Antoine Pitrou]

On Thu, 07 Sep 2017 14:40:33 -0700
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?
> 
> > 
> > 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.

Also, while some/many of us have fast development machines with
performant SSDs, Python can be used in situations where "disk" I/O is
still slow (imagine a Raspberry Pi system or similar, grinding through
a SD card or USB key to load py and pyc files).

Regards

Antoine.