[Python-Dev] ReleaseNode interface in 4XSLT

[Martin v. Loewis]

Currently, 4XSLT has a dependency on the DOM implementation in terms
of memory management (among other dependencies). I'd like to reduce
this dependency, by providing a centralized function that knows how to
release nodes.

In PyXML, I currently use

# Define ReleaseNode in a DOM-independent way
import xml.dom.ext
import xml.dom.minidom
def _releasenode(n):
    if isinstance(n, xml.dom.minidom.Node):
        n.unlink()
    else:
        xml.dom.ext.ReleaseNode(n)

try:
    from Ft.Lib import pDomlette
    def ReleaseNode(n):
        if isinstance(n, pDomlette.Node):
            pDomlette.ReleaseNode(n)
        else:
            _releasenode(n)
    _XsltElementBase = pDomlette.Element
except ImportError:
    ReleaseNode = _releasenode
    from minisupport import _XsltElementBase

This code knows how to release minidom, 4DOM, and pDomlette nodes, and
supports installations without 4Suite (i.e. without pDomlette). I've
put this into xslt/__init__.py, so that all callers of
Ft.Lib.pDomlette.ReleaseNode now need to call xml.xslt.ReleaseNode.
If desired, I could produce a patch against the public Ft CVS.

As a slightly independent question, such a function also ought to
support DOM implementations not known to it; I'm thinking in
particular of the Zope DOMs. I'd like to hear proposals on how such an
interface should work; I see three options:

a) it is an operation on the document node (or any node), as in minidom.
b) it is an operation on the DOM implementation (almost as in 4Suite;
   you'd need to navigate from the node to the implementation, then
   you'd need a well-known operation on the implementation)
c) the code assumes that no release activity is necessary for unknown
   DOMs, effectively believing in reference counting, garbage collection,
   acquisition, and other black art.

Any comments appreciated, in particular
1. from the Ft maintainers on introducing xml.xslt.ReleaseNode, and
2. from authors of other DOMs on a general memory management API for
   Python DOM.

Regards,
Martin