[XML-SIG] XPath and Zope's ParsedXML DOM

[Martijn Faassen]

Hi there,

I've been trying to make XPath work with Zope's DOM implementation,
ParsedXML. In the process I've discovered some incompatibilities in
XPath that I had to hack around.

The problem is as follows. ParsedXML uses DOM nodes that are 
descendants of ExtensionClass. This means that type(node) != types.InstanceType.

Conversions.py depends on this in several places, however. After hacking
around them XPath works better for me.

Here are the two places where I had to hack:

The function CoreStringValue has this line:

result = _strConversions.get(type(object), _strUnknown)(object)

but, since instances now don't trigger the InstanceType key in 
_strConversions, this fails and returns None for valid instances. I've hacked 
around this by doing the following:

if hasattr(object, 'ownerDocument'):
    result = _strInstance(object)
else:
    result = _strConversions.get(type(object), _strUnknown)(object)

I'm not sure if this succeeds in all cases and it's a hack. I'll study
ExtensionClasses to see if there may be a better way.

The other hack is similar and involves the types.ListType entry in the
_strConversions dictionary. Again the lookup that takes place in the
value lambda fails due to ExtensionClass.

Regards,

Martijn