[Import-SIG] PEP for the removal of PYO files

[Brett Cannon]

On Fri, Feb 27, 2015 at 1:28 PM Barry Warsaw <barry at python.org> wrote:

> This looks great Brett, thanks for pushing it forward.  I think it's a
> perfectly natural and consistent extension to PEP 3147.
>
> Some comments inlined.
>
> On Feb 27, 2015, at 05:06 PM, Brett Cannon wrote:
>
> >Rationale
> >=========
> >
> >  - 0: ``.pyc``
> >  - 1 (``-O``): ``.pyo``
> >  - 2 (``-OO``): ``.pyo``
>
> This is all the rationale I need. :)
>
> >The "opt-" prefix was chosen so as to provide a visual separator
> >from the cache tag. The placement of the optimization level after
> >the cache tag was chosen to preserve lexicographic sort order of
> >bytecode file names based on module name and cache tag which will
> >not vary for a single interpreter. The "opt-" prefix was chosen over
> >"o" so as to be somewhat self-documenting. The "opt-" prefix was
> >chosen over "O" so as to not have any confusion with "0" while being
> >so close to the interpreter version number.
>
> I get it, and the examples you include in the open questions is helpful,
> but I
> still don't like "opt-".  We'll no doubt bikeshed on this until Guido
> decides but looking at the examples below I'd be okay with 'O<level>'.  Did
> you consider 'opt<level>', e.g. imporlib.cpython-35.opt0.pyc ?
>

Nope, and I'll think about it and at least add it as a possibility.


>
> >Compatibility Considerations
> >============================
>
> Just as PEP 3147 had to make backward compatibility concessions to .pyc
> files
> living outside __pycache__ (which I think is still supported, right?)


Unfortunately yes.


> I think
> you'll have to do the same for traditional .pyo files, at least for Python
> 3.5.  You won't have to *write* such files, but if they exist and the
> corresponding optimization level pyc file isn't present in __pycache__,
> you'll
> have to load them.
>
> It might in fact make sense to add some language to this PEP saying that in
> Python 3.6, support for old-style .pyc and .pyo files will be removed.
>

Ah, but you see the magic number changed in Python 3.5 for matrix
multiplication, so pre-existing .pyo files won't even load, so they will
have to be regenerated regardless. I will mention that in the PEP.
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