[Webware-devel] class-based config syntax

[Tavis R. <ta...@ca...>]

Geoff,
going back to your class-based config syntax...

The reason we'd need to subclass SettingsContainer is that it is 
possible to have settings that are in fact classes and don't begin 
with an underscore:

##
from SettingsManager import SettingsContainer as SC
class Applications(SC):
    class MyApp(SC):
	class Dirs:  # virtual dirs like <location> in Apache
	    Services = '/home/tavis/MyApp/Services'
	    Products = '/home/tavis/MyApp/Products'
        from Foo import Bar as ApplicationClass 
        from Foo import Whiz as RequestClass 
        from Foo import Bang as SessionStoreClass 
##

Without using something like SettingsContainer those custom classes 
would be treated as if they were SettingsContainers themselves, which 
is definitely not what we want in this case. 

There is another alternative: create a slightly modified Python 
syntax that uses a different keyword than 'class' for 
SettingsContainers. A custom import_hook (via the standarde ihooks.py 
module) would be used to import the config modules:

##
config Applications:
    config MyApp:
	config Dirs:  # virtual dirs like <location> in Apache
	    Services = '/home/tavis/MyApp/Services'
	    Products = '/home/tavis/MyApp/Products'
        from Foo import Bar as ApplicationClass 
        from Foo import Whiz as RequestClass 
        from Foo import Bang as SessionStoreClass 
##

Once the import hook has been loaded, "import WebkitConfig" would 
find WebkitConfig.cfg, translate it to the syntax in the first 
example above and then load it as if it were WebkitConfig.py.  To 
WebKit and the end user it would be seemless.   

We could even get rid of the keyword completely:

##
Applications:
    MyApp:
	Dirs:  # virtual dirs like <location> in Apache
	    Services = '/home/tavis/MyApp/Services'
	    Products = '/home/tavis/MyApp/Products'
        from Foo import Bar as ApplicationClass 
        from Foo import Whiz as RequestClass 
        from Foo import Bang as SessionStoreClass 
##

The advantages would be:
* it's very concise
* ALL other Python syntax would work as expected (even class)
* no need to use the 'class' keyword, which is misleading in this 
situation
* the experienced gained working with the import hooks here would 
transfer to Cheetah and other Webware components that need to build 
servlet factories that load a customized Python syntax

The disadvantages would be:
* it would require bit of work
* we would have to be careful not to create clashes with other import 
hooks, such as the ones used by ZODB.

Quixote uses the technique to load its .ptl template files. Their 
custom import hook module is 152 lines long including comments, so it 
doesn't look very difficult.



In dictionary format these settings would be expressed as:

##
from Foo import Bar as ApplicationClass 
from Foo import Whiz as RequestClass 
from Foo import Bang as SessionStoreClass 
Applications ={'MyApp':{'ApplicationClass':ApplicationClass,
                       'RequestClass':RequestClass,
                       'SessionStoreClass':SessionStoreClass,
		       'Dirs':{'Services':'/home/tavis/MyApp/Services',
                             'Products':'/home/tavis/MyApp/Products',
                              }
                       }
               }
##

Either format would be valid and you would be able to mix the two 
where necessary:

##
from SettingsManager import SettingsContainer as SC
class Applications(SC):
    class MyApp(SC):
	Dirs = {'Services':...,
                'Products':...,
               }
        from Foo import Bar as ApplicationClass 
        from Foo import Whiz as RequestClass 
        from Foo import Bang as SessionStoreClass 
##

Internally Webware would store all settings as dictionaries.

Tavis