Re: helper functions for accepting elementtrees/elements/documents as input

Stefan Behnel wrote:
> I noticed that many of the API classes accept _ElementTree object, although it
> would make just as much sense to apply them to elements or (internally) to
> documents. So here are three helper functions that you can use at the top of
> API functions to check what actually came in and to determine how to extract
> the document that is refered to and the context node within the document.
>
> This simplifies clumsy expressions like
> XSLT(ElementTree(XML("...")))
> and the like to
> XSLT(XML("..."))
>
> I checked them into my branch, although they may need modification later,
> depending on Geerts work.
While I agree that cleaning up how this works might be a good thing, I 
wonder what this means for ElementTree compatibility. I.e. it'll become 
a lot easier to write lxml code that doesn't work in ElementTree.
Perhaps we should check with Fredrik Lundh what he thinks first.

[snip]
> Index: src/lxml/etree.pyx
> ===================================================================
> --- src/lxml/etree.pyx  (Revision 19828)
> +++ src/lxml/etree.pyx  (Arbeitskopie)
> @@ -1093,6 +1093,36 @@
>
>
>  # Private helper functions
> +cdef _Document _documentOrRaise(object input):
> +    cdef _Document doc
> +    doc = _documentOf(input)
> +    if doc is None:
> +        raise TypeError, "Invalid input object: %s" % type(input)
> +    else:
> +        return doc
> +
> +cdef _Document _documentOf(object input):
> +    # call this to get the document of a
> +    # _Document, _ElementTree or _NodeBase object
> +    if isinstance(input, _ElementTree):
> +        return (<_ElementTree>input)._doc
> +    elif isinstance(input, _NodeBase):
> +        return (<_NodeBase>input)._doc
> +    elif isinstance(input, _Document):
> +        return <_Document>input
> +    else:
> +        return None
> +
> +cdef _NodeBase _rootNodeOf(object input):
> +    # call this to get the root node of a
> +    # _Document, _ElementTree or _NodeBase object
> +    if hasattr(input, 'getroot'): # Document/ElementTree
> +        return <_NodeBase>(input.getroot())
> +    elif isinstance(input, _NodeBase):
> +        return <_NodeBase>input
> +    else:
> +        return None
> +
>  cdef xmlDoc* _fakeRootDoc(xmlDoc* c_base_doc, xmlNode* c_node):
>      # build a temporary document that has the given node as root node
>      # note that copy and original must not be modified during its lifetime!!