[Python-Dev] #12982: Should -O be required to *read* .pyo files?

[R. David Murray]

On Wed, 13 Jun 2012 13:19:43 -0400, Brett Cannon <brett at python.org> wrote:
> On Tue, Jun 12, 2012 at 2:16 PM, Terry Reedy <tjreedy at udel.edu> wrote:
> 
> > http://bugs.python.org/**issue12982 <http://bugs.python.org/issue12982>
> >
> > Currently, cpython requires the -O flag to *read* .pyo files as well as
> > the write them. This is a nuisance to people who receive them from others,
> > without the source. The originator of the issue quotes the following from
> > the doc (without giving the location).
[...]
> > So is the import restriction either an accident or obsolete holdover?
> 
> Neither. .pyo files are actually different from .pyc files in terms of what
> bytecode they may emit. Currently -O causes all asserts to be left out of
> the bytecode and -OO leaves out all docstrings on top of what -O does. This
> makes a difference if you are trying to introspect at the interpreter
> prompt or are testing things in development and want those asserts to be
> triggered if needed.
> 
> > If so, can removing it be treated as a bugfix and put into current
> > releases, or should it be treated as an enhancement only for a future
> > release?
> >
> The behaviour shouldn't change. There has been talk of doing even more
> aggressive optimizing under -O, which once again would cause an even larger
> deviation between a .pyo file and a .pyc file (e.g. allowing Python code to
> hook into the peephole optimizer or an entirely new AST optimizer).
> 
> > Or is the restriction an intentional reservation of the possibility of
> > making *execution* depend on the flag? Which would mean that the
> > restriction should be kept and only the doc changed?
> 
> The docs should get updated to be more clear.

OK, but you didn't answer the question :).  If I understand correctly,
everything you said applies to *writing* the bytecode, not reading it.

So, is there any reason to not use the .pyo file (if that's all that is
around) when -O is not specified?

The only technical reason I can see why -O should be required for a .pyo
file to be used (*if* it is the only thing around) is if it won't *run*
without the -O switch.  Is there any expectation that that will ever be
the case?

On the other hand, not wanting make any extra effort to support sourceless
distributions could be a reason as well.  But if that's the case we
should be transparent about it.

--David