Python and the XML Document Object Model (DOM) with 4Suite

Here is the class declaration. Instances contain an attribute named .node that will contain the actual DOM Document node.

# - - - - -   c l a s s   D o c u m e n t   - - - - -

class Document:
    """Represents an XML document.

      State/invariants:
        .doctype:      [ as passed to constructor, read-only ]
        .nsMap:        [ as passed to constructor, read-only ]
        .dom:          [ the DOMImplementation object ]
        .node:         [ the DOM Document node ]
    """

Here's the class constructor:

# - - -   D o c u m e n t . _ _ i n i t _ _   - - -

    def __init__ ( self, rootGI, doctype=None, nsMap=None ):
        """Constructor for Document.

          [ (domlette is Ft.Xml.Domlette) and
            (rootGI is the root element's qualified name) and
            (doctype is a DocumentType object or None) ->
              return a new Document object with a rootGI Element
              child and document type given by doctype ]
        """

        #-- 1 --
        # [ domlette is Ft.Xml.Domlette ->
        #     self.doctype  :=  doctype
        #     self.nsMap    :=  nsMap
        #     self.dom      :=  a DOMImplementation object ]
        self.doctype  =  doctype
        self.nsMap    =  nsMap
        self.dom      =  domlette.implementation

        #-- 2 --
        # [ if rootGI has a namespace prefix that is not a key in
        #   self.nsMap ->
        #     raise KeyError
        #   else if rootGI has a namespace prefix ->
        #     rootNsuri  :=  corresponding namespace URI from
        #                    self.nsMap
        #   else ->
        #     rootNsuri  :=  None ]
        rootNsuri, rootLocal  =  self.splitQName ( rootGI )

        #-- 3 --
        # [ self.dom is a DOMImplementation object ->
        #     self.node  :=  a new DOM Document node with default
        #       namespace and root element rootGI ]
        self.node  =  self.dom.createDocument ( rootNsuri,
                          rootGI, None )

If the caller gave us a DocumentType object, we copy its public and system identifiers over into the DOM Document object.

        #-- 4 --
        if  doctype:
            self.node.publicId  =  doctype.publicId
            self.node.systemId  =  doctype.systemId

Finally, we create the root node. Here, we take advantage of the polymorphism of the Element constructor: it can take a Document object as the parent. In that case, instead of creating a new DOM Document object, it takes the one found in self.node.documentElement and wraps that instead.

        #-- 5 --
        # [ if rootGI has a namespace prefix that is not a key in
        #   nsMap ->
        #     raise KeyError
        #   else ->
        #     self.root  :=  a new Element with qName rootGI ]
        self.root  =  Element ( self, rootGI )