[Python-Dev] PEP 376 proposed changes for basic plugins support

[David Cournapeau]

On Tue, Aug 3, 2010 at 8:48 PM, Antoine Pitrou <solipsis at pitrou.net> wrote:
> On Tue, 03 Aug 2010 10:28:07 +0200
> "M.-A. Lemburg" <mal at egenix.com> wrote:
>> >
>> > Don't forget system packaging tools like .deb, .rpm, etc., which do not
>> > generally take kindly to updating such things.  For better or worse, the
>> > filesystem *is* our "central database" these days.
>>
>> I don't think that's a problem: the SQLite database would be a cache
>> like e.g. a font cache or TCSH command cache, not a replacement of
>> the meta files stored in directories.
>>
>> Such a database would solve many things at once: faster access to
>> the meta-data of installed packages, fewer I/O calls during startup,
>> more flexible ways of doing queries on the meta-data, needed for
>> introspection and discovery, etc.
>
> If the cache can become stale because of system package management
> tools, how do you avoid I/O calls while checking that the database is
> fresh enough at startup?

There is a tension between the two approaches: either you want
"auto-discovery", or you want a system with explicit registration and
only the registered plugins would be visible to the system.

System-wise, I much prefer the later, and auto-discovery should be
left at the application discretion IMO. A library to deal with this at
the *app* level may be fine. But the current system of loading
packages and co is already complex enough in python that anything that
complexify at the system (interpreter) level sounds like a bad idea.

David