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

[Nick Coghlan]

On Wed, Jun 13, 2012 at 11:10 AM, Brett Cannon <brett at python.org> wrote:
>> > 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 seems fine for me too if we don't end up using this
>> flag.
>
> OK, that's 2 votes for that exception.

+ 1 from me as well, both for skipping any implicit reading or writing
of the cache when cache_tag is None (IIRC, that's the use case we had
in mind when we allowed that field to be None in the PEP 421
discussion), and for *explicit* attempts to access the cache when the
tag is None triggering NotImplementedError.

That way people are free to use either LBYL (checking cache_tag) or
EAFP (catching NotImplementedError).

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia