20.7. "xml.dom.minidom" — Minimal DOM implementation
****************************************************

**Source code:** Lib/xml/dom/minidom.py

======================================================================

"xml.dom.minidom" is a minimal implementation of the Document Object
Model interface, with an API similar to that in other languages.  It
is intended to be simpler than the full DOM and also significantly
smaller.  Users who are not already proficient with the DOM should
consider using the "xml.etree.ElementTree" module for their XML
processing instead.

Warning: The "xml.dom.minidom" module is not secure against
  maliciously constructed data.  If you need to parse untrusted or
  unauthenticated data see XML vulnerabilities.

DOM applications typically start by parsing some XML into a DOM.  With
"xml.dom.minidom", this is done through the parse functions:

   from xml.dom.minidom import parse, parseString

   dom1 = parse('c:\\temp\\mydata.xml')  # parse an XML file by name

   datasource = open('c:\\temp\\mydata.xml')
   dom2 = parse(datasource)  # parse an open file

   dom3 = parseString('<myxml>Some data<empty/> some more data</myxml>')

The "parse()" function can take either a filename or an open file
object.

xml.dom.minidom.parse(filename_or_file, parser=None, bufsize=None)

   Return a "Document" from the given input. *filename_or_file* may be
   either a file name, or a file-like object. *parser*, if given, must
   be a SAX2 parser object. This function will change the document
   handler of the parser and activate namespace support; other parser
   configuration (like setting an entity resolver) must have been done
   in advance.

If you have XML in a string, you can use the "parseString()" function
instead:

xml.dom.minidom.parseString(string, parser=None)

   Return a "Document" that represents the *string*. This method
   creates an "io.StringIO" object for the string and passes that on
   to "parse()".

Both functions return a "Document" object representing the content of
the document.

What the "parse()" and "parseString()" functions do is connect an XML
parser with a “DOM builder” that can accept parse events from any SAX
parser and convert them into a DOM tree.  The name of the functions
are perhaps misleading, but are easy to grasp when learning the
interfaces.  The parsing of the document will be completed before
these functions return; it’s simply that these functions do not
provide a parser implementation themselves.

You can also create a "Document" by calling a method on a “DOM
Implementation” object.  You can get this object either by calling the
"getDOMImplementation()" function in the "xml.dom" package or the
"xml.dom.minidom" module.  Once you have a "Document", you can add
child nodes to it to populate the DOM:

   from xml.dom.minidom import getDOMImplementation

   impl = getDOMImplementation()

   newdoc = impl.createDocument(None, "some_tag", None)
   top_element = newdoc.documentElement
   text = newdoc.createTextNode('Some textual content.')
   top_element.appendChild(text)

Once you have a DOM document object, you can access the parts of your
XML document through its properties and methods.  These properties are
defined in the DOM specification.  The main property of the document
object is the "documentElement" property.  It gives you the main
element in the XML document: the one that holds all others.  Here is
an example program:

   dom3 = parseString("<myxml>Some data</myxml>")
   assert dom3.documentElement.tagName == "myxml"

When you are finished with a DOM tree, you may optionally call the
"unlink()" method to encourage early cleanup of the now-unneeded
objects.  "unlink()" is an "xml.dom.minidom"-specific extension to the
DOM API that renders the node and its descendants are essentially
useless.  Otherwise, Python’s garbage collector will eventually take
care of the objects in the tree.

See also:

  Document Object Model (DOM) Level 1 Specification
     The W3C recommendation for the DOM supported by
     "xml.dom.minidom".


20.7.1. DOM Objects
===================

The definition of the DOM API for Python is given as part of the
"xml.dom" module documentation.  This section lists the differences
between the API and "xml.dom.minidom".

Node.unlink()

   Break internal references within the DOM so that it will be garbage
   collected on versions of Python without cyclic GC.  Even when
   cyclic GC is available, using this can make large amounts of memory
   available sooner, so calling this on DOM objects as soon as they
   are no longer needed is good practice.  This only needs to be
   called on the "Document" object, but may be called on child nodes
   to discard children of that node.

   You can avoid calling this method explicitly by using the "with"
   statement. The following code will automatically unlink *dom* when
   the "with" block is exited:

      with xml.dom.minidom.parse(datasource) as dom:
          ... # Work with dom.

Node.writexml(writer, indent="", addindent="", newl="")

   Write XML to the writer object.  The writer should have a "write()"
   method which matches that of the file object interface.  The
   *indent* parameter is the indentation of the current node.  The
   *addindent* parameter is the incremental indentation to use for
   subnodes of the current one.  The *newl* parameter specifies the
   string to use to terminate newlines.

   For the "Document" node, an additional keyword argument *encoding*
   can be used to specify the encoding field of the XML header.

Node.toxml(encoding=None)

   Return a string or byte string containing the XML represented by
   the DOM node.

   With an explicit *encoding* [1] argument, the result is a byte
   string in the specified encoding. With no *encoding* argument, the
   result is a Unicode string, and the XML declaration in the
   resulting string does not specify an encoding. Encoding this string
   in an encoding other than UTF-8 is likely incorrect, since UTF-8 is
   the default encoding of XML.

Node.toprettyxml(indent="", newl="", encoding="")

   Return a pretty-printed version of the document. *indent* specifies
   the indentation string and defaults to a tabulator; *newl*
   specifies the string emitted at the end of each line and defaults
   to "\n".

   The *encoding* argument behaves like the corresponding argument of
   "toxml()".


20.7.2. DOM Example
===================

This example program is a fairly realistic example of a simple
program. In this particular case, we do not take much advantage of the
flexibility of the DOM.

   import xml.dom.minidom

   document = """\
   <slideshow>
   <title>Demo slideshow</title>
   <slide><title>Slide title</title>
   <point>This is a demo</point>
   <point>Of a program for processing slides</point>
   </slide>

   <slide><title>Another demo slide</title>
   <point>It is important</point>
   <point>To have more than</point>
   <point>one slide</point>
   </slide>
   </slideshow>
   """

   dom = xml.dom.minidom.parseString(document)

   def getText(nodelist):
       rc = []
       for node in nodelist:
           if node.nodeType == node.TEXT_NODE:
               rc.append(node.data)
       return ''.join(rc)

   def handleSlideshow(slideshow):
       print("<html>")
       handleSlideshowTitle(slideshow.getElementsByTagName("title")[0])
       slides = slideshow.getElementsByTagName("slide")
       handleToc(slides)
       handleSlides(slides)
       print("</html>")

   def handleSlides(slides):
       for slide in slides:
           handleSlide(slide)

   def handleSlide(slide):
       handleSlideTitle(slide.getElementsByTagName("title")[0])
       handlePoints(slide.getElementsByTagName("point"))

   def handleSlideshowTitle(title):
       print("<title>%s</title>" % getText(title.childNodes))

   def handleSlideTitle(title):
       print("<h2>%s</h2>" % getText(title.childNodes))

   def handlePoints(points):
       print("<ul>")
       for point in points:
           handlePoint(point)
       print("</ul>")

   def handlePoint(point):
       print("<li>%s</li>" % getText(point.childNodes))

   def handleToc(slides):
       for slide in slides:
           title = slide.getElementsByTagName("title")[0]
           print("<p>%s</p>" % getText(title.childNodes))

   handleSlideshow(dom)


20.7.3. minidom and the DOM standard
====================================

The "xml.dom.minidom" module is essentially a DOM 1.0-compatible DOM
with some DOM 2 features (primarily namespace features).

Usage of the DOM interface in Python is straight-forward.  The
following mapping rules apply:

* Interfaces are accessed through instance objects. Applications
  should not instantiate the classes themselves; they should use the
  creator functions available on the "Document" object. Derived
  interfaces support all operations (and attributes) from the base
  interfaces, plus any new operations.

* Operations are used as methods. Since the DOM uses only "in"
  parameters, the arguments are passed in normal order (from left to
  right). There are no optional arguments. "void" operations return
  "None".

* IDL attributes map to instance attributes. For compatibility with
  the OMG IDL language mapping for Python, an attribute "foo" can also
  be accessed through accessor methods "_get_foo()" and "_set_foo()".
  "readonly" attributes must not be changed; this is not enforced at
  runtime.

* The types "short int", "unsigned int", "unsigned long long", and
  "boolean" all map to Python integer objects.

* The type "DOMString" maps to Python strings. "xml.dom.minidom"
  supports either bytes or strings, but will normally produce strings.
  Values of type "DOMString" may also be "None" where allowed to have
  the IDL "null" value by the DOM specification from the W3C.

* "const" declarations map to variables in their respective scope
  (e.g. "xml.dom.minidom.Node.PROCESSING_INSTRUCTION_NODE"); they must
  not be changed.

* "DOMException" is currently not supported in "xml.dom.minidom".
  Instead, "xml.dom.minidom" uses standard Python exceptions such as
  "TypeError" and "AttributeError".

* "NodeList" objects are implemented using Python’s built-in list
  type. These objects provide the interface defined in the DOM
  specification, but with earlier versions of Python they do not
  support the official API.  They are, however, much more “Pythonic”
  than the interface defined in the W3C recommendations.

The following interfaces have no implementation in "xml.dom.minidom":

* "DOMTimeStamp"

* "DocumentType"

* "DOMImplementation"

* "CharacterData"

* "CDATASection"

* "Notation"

* "Entity"

* "EntityReference"

* "DocumentFragment"

Most of these reflect information in the XML document that is not of
general utility to most DOM users.

-[ Footnotes ]-

[1] The encoding name included in the XML output should conform to
    the appropriate standards. For example, “UTF-8” is valid, but
    “UTF8” is not valid in an XML document’s declaration, even though
    Python accepts it as an encoding name. See
    https://www.w3.org/TR/2006 /REC-xml11-20060816/#NT-EncodingDecl
    and https://www.iana.org/assignments/character-sets/character-
    sets.xhtml.
