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authorcinap_lenrek <cinap_lenrek@localhost>2011-05-03 11:25:13 +0000
committercinap_lenrek <cinap_lenrek@localhost>2011-05-03 11:25:13 +0000
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+\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 the
+Document Object Model interface. It is intended to be
+simpler 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 open
+file 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 the
+content of the document.
+
+What the \function{parse()} and \function{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 \class{Document} by calling a method on a ``DOM
+Implementation'' object. You can get this object either by calling
+the \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 will
+always return a \class{Document} instance from the minidom
+implementation, while the version from \refmodule{xml.dom} may provide
+an alternate implementation (this is likely if you have the
+\ulink{PyXML package}{http://pyxml.sourceforge.net/} installed). Once
+you have a \class{Document}, you can add child nodes to it to populate
+the DOM:
+
+\begin{verbatim}
+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)
+\end{verbatim}
+
+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 \member{documentElement} property. It gives you the
+main element in the XML document: the one that holds all others. Here
+is 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 is
+necessary because some versions of Python do not support garbage
+collection of objects that refer to each other in a cycle. Until this
+restriction is removed from all versions of Python, it is safest to
+write 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 to
+the DOM API. After calling \method{unlink()} on a node, the node and
+its 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 the
+differences between the API and \refmodule{xml.dom.minidom}.
+
+
+\begin{methoddesc}[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
+\class{Document} object, but may be called on child nodes to discard
+children 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 object
+interface. The \var{indent} parameter is the indentation of the current
+node. The \var{addindent} parameter is the incremental indentation to use
+for subnodes of the current one. The \var{newl} parameter specifies the
+string to use to terminate newlines.
+
+\versionchanged[The optional keyword parameters
+\var{indent}, \var{addindent}, and \var{newl} were added to support pretty
+output]{2.1}
+
+\versionchanged[For the \class{Document} node, an additional keyword
+argument \var{encoding} can be used to specify the encoding field of the XML
+header]{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 the
+result is Unicode string if the default encoding cannot represent all
+characters in the document. Encoding this string in an encoding other
+than UTF-8 is likely incorrect, since UTF-8 is the default encoding of
+XML.
+
+With an explicit \var{encoding} argument, the result is a byte string
+in the specified encoding. It is recommended that this argument is
+always specified. To avoid \exception{UnicodeError} exceptions in case of
+unrepresentable text data, the encoding argument should be specified
+as "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} specifies
+the indentation string and defaults to a tabulator; \var{newl} specifies
+the 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 seriously
+broken. 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 simple
+program. In this particular case, we do not take much advantage
+of 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 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:
+
+\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 of
+general utility to most DOM users.