[Python-Dev] [compatibility-sig] making sure importlib.machinery.SourceLoader doesn't throw an exception if bytecode is not supported by a VM

[Jeff Hardy]

On Tue, Jun 12, 2012 at 12:01 PM, Brett Cannon <brett at python.org> wrote:
> On Tue, Jun 12, 2012 at 2:28 PM, Eric Snow <ericsnowcurrently at gmail.com>
> wrote:
>>
>> On Tue, Jun 12, 2012 at 10:48 AM, Brett Cannon <brett at python.org> wrote:
>> > I should mention another option is to add sys.dont_read_bytecode (I
>> > think I
>> > have discussed this with Frank at some point).
>>
>> Or check for "sys.implementation.cache_tag is None"...
>
>
> Perfect! Will that work for Jython (Franke) and IronPython (Jeff)?

IronPython will probably never *write* pyc files, but it might *read*
them at some point -- as I understand cache_tag, we'd set it to
whatever version of CPython's pyc files we could read (that seems to
violate the spirit of sys.implementation). The combination of that and
sys.dont_write_bytecode should cover all of the states; I'll just lock
down sys.dont_write_bytecode so that changes are completely ignored.

>
> This does mean, though, that imp.cache_from_source() and
> imp.source_from_cache() might need to be updated to raise a reasonable
> exception when sys.implementation.cache_tag is set to None as I believe
> right now it will raise a TypeError because None isn't a str. But what to
> raise instead? TypeError? EnvironmentError?

NotImplementedError?

- Jeff