[XML-SIG] Providing a DOMImplementationFactory

[Uche Ogbuji]

> The DOM level 3 draft proposes a mechanism for Java to locate a
> DOMImplementation object. In short, Java programs can invoke
> 
>    org.w3c.dom.DOMImplementationFactory.getDOMImplementation()
> 
> which loads the implementation defined in the property
> org.w3c.dom.DOMImplementation. Should Python offer a similar
> mechanism? If so, how should it work?
> 
> I can think of the following strategy:
> - offer two functions, 
>   xml.dom.getDOMImplementation([name])
>   xml.dom.registerDOMImplementation(name, implementation)
> 
>   That is not really a factory, but rather a locator (should that be
>   an implementation factory?)

I think it should be a factory, because I've just been thinking about the 
ability to set properties non-globally on DOM implementations.  For instance, 
I think 4DOM should come with the mutation event system disabled unless 
support for this is set as a property.

A factory would be a perfect place to set such properties.

> - In getDOMImplementation, use various approaches of returning an
>   implementation:
>   * if a name was given, and an implementation with that name was
>     registered, return it. Well-known names should be published by
>     posting to xml-sig@python.org, and subsequently recorded in
>     xml.dom.__init__
>   * if no name is given, but the PYTHON_DOM environment variable is set,
>     this variable names a module which should have an .implementation
>     attribute; this is then used. I don't know whether it is good or bad
>     that Python does not provide Java-style properties...
>   * if no name was given, and attempt to return a "best" implementation
>     should be done, where best means "most featureful". Not sure how
>     to compute this, though.
> 
> - The implementation of xml.dom.__init__ would provide a number of
>   pre-registered DOM implementations, which would always include
>   minidom and would include 4DOM if PyXML is installed.
> 
> - add-on packages (like 4Suite, or Zope) can install .pth files which
>   register additional DOM implementations (starting with Python 2.1).

Sounds good enough to try out.


-- 
Uche Ogbuji                               Principal Consultant
uche.ogbuji@fourthought.com               +1 303 583 9900 x 101
Fourthought, Inc.                         http://Fourthought.com 
4735 East Walnut St, Ste. C, Boulder, CO 80301-2537, USA
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