[Chandler-dev] Re: Parcel loading vs. Egg loading

[Phillip J. Eby]

At 12:09 PM 6/8/2006 -0700, John Anderson wrote:
>I was talking to Markku today and we thought it would be useful to have a 
>4-way Skype conversation to discuss parcel loading and egg loading as it 
>related to discovering the internationalization files. So, how about 
>meeting via Skype tomorrow morning, say 9:30 AM?

In the interest of moving more of this kind of information to the 
development lists, I'd just like to go ahead and propose what I think 
Chandler should do to load the internationalization data, using a mechanism 
based on Markku's work so far.

Markku currently has code (if I understand correctly) that loops over the 
eggs on sys.path and builds an index, something like:

     from pkg_resources import working_set

     for egg in working_set:
         if egg.has_metadata('resource.info'):
             # code here to update the registry of resource
             # information by reading the 'resource.info' from
             # the egg

What I would propose doing is to change this code to read instead:

     from pkg_resources import working_set, add_activation_listener

     @add_activation_listener
     def update_resources(egg):
         if egg.has_metadata('resource.info'):
             # code here to update the registry of resource
             # information by reading the 'resource.info' from
             # the egg

What this code will do, is that whenever an egg is "activated" (added to 
sys.path), its resources will be immediately detected and loaded.

Thus, any eggs that are on sys.path when Chandler starts, will have their 
resources detected immediately (because add_activation_listener calls the 
callback immediately for eggs that are *already* on sys.path).  Any that 
are loaded later (e.g. by the parcel loader scanning PARCELPATH for more 
eggs) will automatically cause the resource registry to be updated, as the 
egg runtime will call the callback routine as shown above.

As a side effect, if we later add the ability to download and install eggs 
while Chandler is running, any resources they define will also be registered.

Does this answer the questions that you had in mind for the meeting, or was 
there something else you wanted to cover?