\section{\module{xml.dom.minidom} ---         Lightweight DOM implementation} \declaremodule{standard}{xml.dom.minidom}\modulesynopsis{Lightweight Document Object Model (DOM) implementation.}\moduleauthor{Paul Prescod}{paul@prescod.net}\sectionauthor{Paul Prescod}{paul@prescod.net}\sectionauthor{Martin v. L\"owis}{martin@v.loewis.de} \versionadded{2.0} \module{xml.dom.minidom} is a light-weight implementation of theDocument Object Model interface.  It is intended to besimpler than the full DOM and also significantly smaller. DOM applications typically start by parsing some XML into a DOM.  With\module{xml.dom.minidom}, this is done through the parse functions: \begin{verbatim}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>')\end{verbatim} The \function{parse()} function can take either a filename or an openfile object. \begin{funcdesc}{parse}{filename_or_file{, parser}}  Return a \class{Document} from the given input. \var{filename_or_file}  may be either a file name, or a file-like object. \var{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.\end{funcdesc} If you have XML in a string, you can use the\function{parseString()} function instead: \begin{funcdesc}{parseString}{string\optional{, parser}}  Return a \class{Document} that represents the \var{string}. This  method creates a \class{StringIO} object for the string and passes  that on to \function{parse}.\end{funcdesc} Both functions return a \class{Document} object representing thecontent of the document. What the \function{parse()} and \function{parseString()} functions dois connect an XML parser with a ``DOM builder'' that can accept parseevents from any SAX parser and convert them into a DOM tree.  The nameof the functions are perhaps misleading, but are easy to grasp whenlearning the interfaces.  The parsing of the document will becompleted before these functions return; it's simply that thesefunctions do not provide a parser implementation themselves. You can also create a \class{Document} by calling a method on a ``DOMImplementation'' object.  You can get this object either by callingthe \function{getDOMImplementation()} function in the\refmodule{xml.dom} package or the \module{xml.dom.minidom} module.Using the implementation from the \module{xml.dom.minidom} module willalways return a \class{Document} instance from the minidomimplementation, while the version from \refmodule{xml.dom} may providean alternate implementation (this is likely if you have the\ulink{PyXML package}{http://pyxml.sourceforge.net/} installed).  Onceyou have a \class{Document}, you can add child nodes to it to populatethe DOM: \begin{verbatim}from xml.dom.minidom import getDOMImplementation impl = getDOMImplementation() newdoc = impl.createDocument(None, "some_tag", None)top_element = newdoc.documentElementtext = newdoc.createTextNode('Some textual content.')top_element.appendChild(text)\end{verbatim} Once you have a DOM document object, you can access the parts of yourXML document through its properties and methods.  These properties aredefined in the DOM specification.  The main property of the documentobject is the \member{documentElement} property.  It gives you themain element in the XML document: the one that holds all others.  Hereis an example program: \begin{verbatim}dom3 = parseString("<myxml>Some data</myxml>")assert dom3.documentElement.tagName == "myxml"\end{verbatim} When you are finished with a DOM, you should clean it up.  This isnecessary because some versions of Python do not support garbagecollection of objects that refer to each other in a cycle.  Until thisrestriction is removed from all versions of Python, it is safest towrite your code as if cycles would not be cleaned up. The way to clean up a DOM is to call its \method{unlink()} method: \begin{verbatim}dom1.unlink()dom2.unlink()dom3.unlink()\end{verbatim} \method{unlink()} is a \module{xml.dom.minidom}-specific extension tothe DOM API.  After calling \method{unlink()} on a node, the node andits descendants are essentially useless. \begin{seealso}  \seetitle[http://www.w3.org/TR/REC-DOM-Level-1/]{Document Object            Model (DOM) Level 1 Specification}           {The W3C recommendation for the            DOM supported by \module{xml.dom.minidom}.}\end{seealso}  \subsection{DOM Objects \label{dom-objects}} The definition of the DOM API for Python is given as part of the\refmodule{xml.dom} module documentation.  This section lists thedifferences between the API and \refmodule{xml.dom.minidom}.  \begin{methoddesc}[Node]{unlink}{}Break internal references within the DOM so that it will be garbagecollected on versions of Python without cyclic GC.  Even when cyclicGC is available, using this can make large amounts of memory availablesooner, so calling this on DOM objects as soon as they are no longerneeded is good practice.  This only needs to be called on the\class{Document} object, but may be called on child nodes to discardchildren of that node.\end{methoddesc} \begin{methoddesc}[Node]{writexml}{writer\optional{,indent=""\optional{,addindent=""\optional{,newl=""}}}}Write XML to the writer object.  The writer should have a\method{write()} method which matches that of the file objectinterface.  The \var{indent} parameter is the indentation of the currentnode.  The \var{addindent} parameter is the incremental indentation to usefor subnodes of the current one.  The \var{newl} parameter specifies thestring to use to terminate newlines. \versionchanged[The optional keyword parameters\var{indent}, \var{addindent}, and \var{newl} were added to support prettyoutput]{2.1} \versionchanged[For the \class{Document} node, an additional keywordargument \var{encoding} can be used to specify the encoding field of the XMLheader]{2.3}\end{methoddesc} \begin{methoddesc}[Node]{toxml}{\optional{encoding}}Return the XML that the DOM represents as a string. With no argument, the XML header does not specify an encoding, and theresult is Unicode string if the default encoding cannot represent allcharacters in the document. Encoding this string in an encoding otherthan UTF-8 is likely incorrect, since UTF-8 is the default encoding ofXML. With an explicit \var{encoding} argument, the result is a byte stringin the specified encoding. It is recommended that this argument isalways specified. To avoid \exception{UnicodeError} exceptions in case ofunrepresentable text data, the encoding argument should be specifiedas "utf-8". \versionchanged[the \var{encoding} argument was introduced]{2.3}\end{methoddesc} \begin{methoddesc}[Node]{toprettyxml}{\optional{indent\optional{, newl}}}Return a pretty-printed version of the document. \var{indent} specifiesthe indentation string and defaults to a tabulator; \var{newl} specifiesthe string emitted at the end of each line and defaults to \code{\e n}. \versionadded{2.1}\versionchanged[the encoding argument; see \method{toxml()}]{2.3}\end{methoddesc} The following standard DOM methods have special considerations with\refmodule{xml.dom.minidom}: \begin{methoddesc}[Node]{cloneNode}{deep}Although this method was present in the version of\refmodule{xml.dom.minidom} packaged with Python 2.0, it was seriouslybroken.  This has been corrected for subsequent releases.\end{methoddesc}  \subsection{DOM Example \label{dom-example}} This example program is a fairly realistic example of a simpleprogram. In this particular case, we do not take much advantageof the flexibility of the DOM. \verbatiminput{minidom-example.py}  \subsection{minidom and the DOM standard \label{minidom-and-dom}} The \refmodule{xml.dom.minidom} module is essentially a DOM1.0-compatible DOM with some DOM 2 features (primarily namespacefeatures). Usage of the DOM interface in Python is straight-forward.  Thefollowing mapping rules apply: \begin{itemize}\item Interfaces are accessed through instance objects. Applications      should not instantiate the classes themselves; they should use      the creator functions available on the \class{Document} object.      Derived interfaces support all operations (and attributes) from      the base interfaces, plus any new operations. \item Operations are used as methods. Since the DOM uses only      \keyword{in} parameters, the arguments are passed in normal      order (from left to right).   There are no optional      arguments. \keyword{void} operations return \code{None}. \item IDL attributes map to instance attributes. For compatibility      with the OMG IDL language mapping for Python, an attribute      \code{foo} can also be accessed through accessor methods      \method{_get_foo()} and \method{_set_foo()}.  \keyword{readonly}      attributes must not be changed; this is not enforced at      runtime. \item The types \code{short int}, \code{unsigned int}, \code{unsigned      long long}, and \code{boolean} all map to Python integer      objects. \item The type \code{DOMString} maps to Python strings.      \refmodule{xml.dom.minidom} supports either byte or Unicode      strings, but will normally produce Unicode strings.  Values      of type \code{DOMString} may also be \code{None} where allowed      to have the IDL \code{null} value by the DOM specification from      the W3C. \item \keyword{const} declarations map to variables in their      respective scope      (e.g. \code{xml.dom.minidom.Node.PROCESSING_INSTRUCTION_NODE});      they must not be changed. \item \code{DOMException} is currently not supported in      \refmodule{xml.dom.minidom}.  Instead,      \refmodule{xml.dom.minidom} uses standard Python exceptions such      as \exception{TypeError} and \exception{AttributeError}. \item \class{NodeList} objects are implemented using Python's built-in      list type.  Starting with Python 2.2, 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.\end{itemize}  The following interfaces have no implementation in\refmodule{xml.dom.minidom}: \begin{itemize}\item \class{DOMTimeStamp} \item \class{DocumentType} (added in Python 2.1) \item \class{DOMImplementation} (added in Python 2.1) \item \class{CharacterData} \item \class{CDATASection} \item \class{Notation} \item \class{Entity} \item \class{EntityReference} \item \class{DocumentFragment}\end{itemize} Most of these reflect information in the XML document that is not ofgeneral utility to most DOM users.