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

[M.-A. Lemburg]

P.J. Eby wrote:
> At 10:37 PM 8/2/2010 +0200, M.-A. Lemburg wrote:
>> If that's the case, then it would be better to come up with an
>> idea of how to make access to that meta-data available in a less
>> I/O intense way, e.g. by having pip or other package managers update
>> a central SQLite database cache of the data found on disk.
> 
> 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.

> Btw, while adding PLUGINS to PEP 376 is a new proposal, it's essentially
> another spelling of the existing entry_points.txt used by eggs; it
> changes the format to csv instead of .ini, and adds "description" and
> "type" fields, but drops requirements information and I'm not sure if it
> can point to arbitrary objects the way entry_points.txt can.
> 
> Anyway, entry_points.txt has been around enough years in the field that
> the concept itself can't really be called "new" - it's actually quite
> proven.  Checking
> http://nullege.com/codes/search/pkg_resources.iter_entry_points/call , I
> find 187 modules using just that one entry points API.
> 
> Some projects do have more than one module loading plugins, but the
> majority of those 187 appear to be different projects.
> 
> Note that that's modules *loading plugins*, not plugins being
> provided...  so the total number of PyPI projects using entry points in
> some way is likely much higher, once you add in the plugins that these
> 187 lookups are, well, looking up.

setuptools entry points are just one way of doing plugins. There
are other such systems that work well and which do not require
any special administration or setup, simply because the application
using the plugins defines the plugin protocol.

Since you are into comparing numbers, you might want to count
the number of Zope plugins that are available on PyPI and its plugin
system has been around much longer than setuptools has been.
I don't think that proves anything, though.

I simply don't see a good reason to complicate the Python
packaging system by trying to add a particular plugin support
to it.

Plugins are application scope features and should be treated
as such.

-- 
Marc-Andre Lemburg
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