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1034 lines
39 KiB
ReStructuredText
1034 lines
39 KiB
ReStructuredText
:mod:`xml.dom` --- The Document Object Model API
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================================================
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.. module:: xml.dom
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:synopsis: Document Object Model API for Python.
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.. sectionauthor:: Paul Prescod <paul@prescod.net>
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.. sectionauthor:: Martin v. Löwis <martin@v.loewis.de>
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**Source code:** :source:`Lib/xml/dom/__init__.py`
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--------------
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The Document Object Model, or "DOM," is a cross-language API from the World Wide
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Web Consortium (W3C) for accessing and modifying XML documents. A DOM
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implementation presents an XML document as a tree structure, or allows client
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code to build such a structure from scratch. It then gives access to the
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structure through a set of objects which provided well-known interfaces.
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The DOM is extremely useful for random-access applications. SAX only allows you
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a view of one bit of the document at a time. If you are looking at one SAX
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element, you have no access to another. If you are looking at a text node, you
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have no access to a containing element. When you write a SAX application, you
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need to keep track of your program's position in the document somewhere in your
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own code. SAX does not do it for you. Also, if you need to look ahead in the
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XML document, you are just out of luck.
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Some applications are simply impossible in an event driven model with no access
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to a tree. Of course you could build some sort of tree yourself in SAX events,
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but the DOM allows you to avoid writing that code. The DOM is a standard tree
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representation for XML data.
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The Document Object Model is being defined by the W3C in stages, or "levels" in
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their terminology. The Python mapping of the API is substantially based on the
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DOM Level 2 recommendation.
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.. What if your needs are somewhere between SAX and the DOM? Perhaps
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you cannot afford to load the entire tree in memory but you find the
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SAX model somewhat cumbersome and low-level. There is also a module
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called xml.dom.pulldom that allows you to build trees of only the
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parts of a document that you need structured access to. It also has
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features that allow you to find your way around the DOM.
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See http://www.prescod.net/python/pulldom
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DOM applications typically start by parsing some XML into a DOM. How this is
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accomplished is not covered at all by DOM Level 1, and Level 2 provides only
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limited improvements: There is a :class:`DOMImplementation` object class which
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provides access to :class:`Document` creation methods, but no way to access an
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XML reader/parser/Document builder in an implementation-independent way. There
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is also no well-defined way to access these methods without an existing
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:class:`Document` object. In Python, each DOM implementation will provide a
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function :func:`getDOMImplementation`. DOM Level 3 adds a Load/Store
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specification, which defines an interface to the reader, but this is not yet
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available in the Python standard library.
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Once you have a DOM document object, you can access the parts of your XML
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document through its properties and methods. These properties are defined in
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the DOM specification; this portion of the reference manual describes the
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interpretation of the specification in Python.
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The specification provided by the W3C defines the DOM API for Java, ECMAScript,
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and OMG IDL. The Python mapping defined here is based in large part on the IDL
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version of the specification, but strict compliance is not required (though
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implementations are free to support the strict mapping from IDL). See section
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:ref:`dom-conformance` for a detailed discussion of mapping requirements.
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.. seealso::
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`Document Object Model (DOM) Level 2 Specification <https://www.w3.org/TR/2000/REC-DOM-Level-2-Core-20001113/>`_
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The W3C recommendation upon which the Python DOM API is based.
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`Document Object Model (DOM) Level 1 Specification <https://www.w3.org/TR/REC-DOM-Level-1/>`_
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The W3C recommendation for the DOM supported by :mod:`xml.dom.minidom`.
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`Python Language Mapping Specification <http://www.omg.org/cgi-bin/doc?formal/02-11-05.pdf>`_
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This specifies the mapping from OMG IDL to Python.
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Module Contents
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---------------
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The :mod:`xml.dom` contains the following functions:
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.. function:: registerDOMImplementation(name, factory)
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Register the *factory* function with the name *name*. The factory function
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should return an object which implements the :class:`DOMImplementation`
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interface. The factory function can return the same object every time, or a new
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one for each call, as appropriate for the specific implementation (e.g. if that
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implementation supports some customization).
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.. function:: getDOMImplementation(name=None, features=())
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Return a suitable DOM implementation. The *name* is either well-known, the
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module name of a DOM implementation, or ``None``. If it is not ``None``, imports
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the corresponding module and returns a :class:`DOMImplementation` object if the
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import succeeds. If no name is given, and if the environment variable
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:envvar:`PYTHON_DOM` is set, this variable is used to find the implementation.
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If name is not given, this examines the available implementations to find one
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with the required feature set. If no implementation can be found, raise an
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:exc:`ImportError`. The features list must be a sequence of ``(feature,
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version)`` pairs which are passed to the :meth:`hasFeature` method on available
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:class:`DOMImplementation` objects.
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Some convenience constants are also provided:
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.. data:: EMPTY_NAMESPACE
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The value used to indicate that no namespace is associated with a node in the
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DOM. This is typically found as the :attr:`namespaceURI` of a node, or used as
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the *namespaceURI* parameter to a namespaces-specific method.
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.. data:: XML_NAMESPACE
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The namespace URI associated with the reserved prefix ``xml``, as defined by
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`Namespaces in XML <https://www.w3.org/TR/REC-xml-names/>`_ (section 4).
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.. data:: XMLNS_NAMESPACE
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The namespace URI for namespace declarations, as defined by `Document Object
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Model (DOM) Level 2 Core Specification
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<https://www.w3.org/TR/DOM-Level-2-Core/core.html>`_ (section 1.1.8).
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.. data:: XHTML_NAMESPACE
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The URI of the XHTML namespace as defined by `XHTML 1.0: The Extensible
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HyperText Markup Language <https://www.w3.org/TR/xhtml1/>`_ (section 3.1.1).
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In addition, :mod:`xml.dom` contains a base :class:`Node` class and the DOM
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exception classes. The :class:`Node` class provided by this module does not
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implement any of the methods or attributes defined by the DOM specification;
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concrete DOM implementations must provide those. The :class:`Node` class
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provided as part of this module does provide the constants used for the
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:attr:`nodeType` attribute on concrete :class:`Node` objects; they are located
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within the class rather than at the module level to conform with the DOM
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specifications.
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.. Should the Node documentation go here?
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.. _dom-objects:
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Objects in the DOM
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------------------
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The definitive documentation for the DOM is the DOM specification from the W3C.
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Note that DOM attributes may also be manipulated as nodes instead of as simple
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strings. It is fairly rare that you must do this, however, so this usage is not
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yet documented.
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+--------------------------------+-----------------------------------+---------------------------------+
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| Interface | Section | Purpose |
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+================================+===================================+=================================+
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| :class:`DOMImplementation` | :ref:`dom-implementation-objects` | Interface to the underlying |
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| | | implementation. |
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+--------------------------------+-----------------------------------+---------------------------------+
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| :class:`Node` | :ref:`dom-node-objects` | Base interface for most objects |
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| | | in a document. |
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+--------------------------------+-----------------------------------+---------------------------------+
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| :class:`NodeList` | :ref:`dom-nodelist-objects` | Interface for a sequence of |
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| | | nodes. |
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+--------------------------------+-----------------------------------+---------------------------------+
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| :class:`DocumentType` | :ref:`dom-documenttype-objects` | Information about the |
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| | | declarations needed to process |
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| | | a document. |
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+--------------------------------+-----------------------------------+---------------------------------+
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| :class:`Document` | :ref:`dom-document-objects` | Object which represents an |
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| | | entire document. |
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+--------------------------------+-----------------------------------+---------------------------------+
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| :class:`Element` | :ref:`dom-element-objects` | Element nodes in the document |
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| | | hierarchy. |
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+--------------------------------+-----------------------------------+---------------------------------+
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| :class:`Attr` | :ref:`dom-attr-objects` | Attribute value nodes on |
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| | | element nodes. |
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+--------------------------------+-----------------------------------+---------------------------------+
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| :class:`Comment` | :ref:`dom-comment-objects` | Representation of comments in |
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| | | the source document. |
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+--------------------------------+-----------------------------------+---------------------------------+
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| :class:`Text` | :ref:`dom-text-objects` | Nodes containing textual |
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| | | content from the document. |
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+--------------------------------+-----------------------------------+---------------------------------+
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| :class:`ProcessingInstruction` | :ref:`dom-pi-objects` | Processing instruction |
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| | | representation. |
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+--------------------------------+-----------------------------------+---------------------------------+
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An additional section describes the exceptions defined for working with the DOM
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in Python.
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.. _dom-implementation-objects:
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DOMImplementation Objects
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^^^^^^^^^^^^^^^^^^^^^^^^^
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The :class:`DOMImplementation` interface provides a way for applications to
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determine the availability of particular features in the DOM they are using.
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DOM Level 2 added the ability to create new :class:`Document` and
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:class:`DocumentType` objects using the :class:`DOMImplementation` as well.
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.. method:: DOMImplementation.hasFeature(feature, version)
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Return ``True`` if the feature identified by the pair of strings *feature* and
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*version* is implemented.
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.. method:: DOMImplementation.createDocument(namespaceUri, qualifiedName, doctype)
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Return a new :class:`Document` object (the root of the DOM), with a child
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:class:`Element` object having the given *namespaceUri* and *qualifiedName*. The
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*doctype* must be a :class:`DocumentType` object created by
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:meth:`createDocumentType`, or ``None``. In the Python DOM API, the first two
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arguments can also be ``None`` in order to indicate that no :class:`Element`
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child is to be created.
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.. method:: DOMImplementation.createDocumentType(qualifiedName, publicId, systemId)
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Return a new :class:`DocumentType` object that encapsulates the given
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*qualifiedName*, *publicId*, and *systemId* strings, representing the
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information contained in an XML document type declaration.
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.. _dom-node-objects:
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Node Objects
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^^^^^^^^^^^^
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All of the components of an XML document are subclasses of :class:`Node`.
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.. attribute:: Node.nodeType
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An integer representing the node type. Symbolic constants for the types are on
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the :class:`Node` object: :const:`ELEMENT_NODE`, :const:`ATTRIBUTE_NODE`,
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:const:`TEXT_NODE`, :const:`CDATA_SECTION_NODE`, :const:`ENTITY_NODE`,
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:const:`PROCESSING_INSTRUCTION_NODE`, :const:`COMMENT_NODE`,
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:const:`DOCUMENT_NODE`, :const:`DOCUMENT_TYPE_NODE`, :const:`NOTATION_NODE`.
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This is a read-only attribute.
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.. attribute:: Node.parentNode
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The parent of the current node, or ``None`` for the document node. The value is
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always a :class:`Node` object or ``None``. For :class:`Element` nodes, this
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will be the parent element, except for the root element, in which case it will
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be the :class:`Document` object. For :class:`Attr` nodes, this is always
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``None``. This is a read-only attribute.
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.. attribute:: Node.attributes
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A :class:`NamedNodeMap` of attribute objects. Only elements have actual values
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for this; others provide ``None`` for this attribute. This is a read-only
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attribute.
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.. attribute:: Node.previousSibling
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The node that immediately precedes this one with the same parent. For
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instance the element with an end-tag that comes just before the *self*
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element's start-tag. Of course, XML documents are made up of more than just
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elements so the previous sibling could be text, a comment, or something else.
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If this node is the first child of the parent, this attribute will be
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``None``. This is a read-only attribute.
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.. attribute:: Node.nextSibling
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The node that immediately follows this one with the same parent. See also
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:attr:`previousSibling`. If this is the last child of the parent, this
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attribute will be ``None``. This is a read-only attribute.
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.. attribute:: Node.childNodes
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A list of nodes contained within this node. This is a read-only attribute.
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.. attribute:: Node.firstChild
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The first child of the node, if there are any, or ``None``. This is a read-only
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attribute.
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.. attribute:: Node.lastChild
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The last child of the node, if there are any, or ``None``. This is a read-only
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attribute.
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.. attribute:: Node.localName
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The part of the :attr:`tagName` following the colon if there is one, else the
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entire :attr:`tagName`. The value is a string.
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.. attribute:: Node.prefix
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The part of the :attr:`tagName` preceding the colon if there is one, else the
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empty string. The value is a string, or ``None``.
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.. attribute:: Node.namespaceURI
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The namespace associated with the element name. This will be a string or
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``None``. This is a read-only attribute.
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.. attribute:: Node.nodeName
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This has a different meaning for each node type; see the DOM specification for
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details. You can always get the information you would get here from another
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property such as the :attr:`tagName` property for elements or the :attr:`name`
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property for attributes. For all node types, the value of this attribute will be
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either a string or ``None``. This is a read-only attribute.
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.. attribute:: Node.nodeValue
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This has a different meaning for each node type; see the DOM specification for
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details. The situation is similar to that with :attr:`nodeName`. The value is
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a string or ``None``.
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.. method:: Node.hasAttributes()
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Return ``True`` if the node has any attributes.
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.. method:: Node.hasChildNodes()
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Return ``True`` if the node has any child nodes.
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.. method:: Node.isSameNode(other)
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Return ``True`` if *other* refers to the same node as this node. This is especially
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useful for DOM implementations which use any sort of proxy architecture (because
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more than one object can refer to the same node).
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.. note::
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This is based on a proposed DOM Level 3 API which is still in the "working
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draft" stage, but this particular interface appears uncontroversial. Changes
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from the W3C will not necessarily affect this method in the Python DOM interface
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(though any new W3C API for this would also be supported).
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.. method:: Node.appendChild(newChild)
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Add a new child node to this node at the end of the list of
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children, returning *newChild*. If the node was already in
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the tree, it is removed first.
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.. method:: Node.insertBefore(newChild, refChild)
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Insert a new child node before an existing child. It must be the case that
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*refChild* is a child of this node; if not, :exc:`ValueError` is raised.
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*newChild* is returned. If *refChild* is ``None``, it inserts *newChild* at the
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end of the children's list.
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.. method:: Node.removeChild(oldChild)
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Remove a child node. *oldChild* must be a child of this node; if not,
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:exc:`ValueError` is raised. *oldChild* is returned on success. If *oldChild*
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will not be used further, its :meth:`unlink` method should be called.
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.. method:: Node.replaceChild(newChild, oldChild)
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Replace an existing node with a new node. It must be the case that *oldChild*
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is a child of this node; if not, :exc:`ValueError` is raised.
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.. method:: Node.normalize()
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Join adjacent text nodes so that all stretches of text are stored as single
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:class:`Text` instances. This simplifies processing text from a DOM tree for
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many applications.
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.. method:: Node.cloneNode(deep)
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Clone this node. Setting *deep* means to clone all child nodes as well. This
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returns the clone.
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.. _dom-nodelist-objects:
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NodeList Objects
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^^^^^^^^^^^^^^^^
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A :class:`NodeList` represents a sequence of nodes. These objects are used in
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two ways in the DOM Core recommendation: an :class:`Element` object provides
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one as its list of child nodes, and the :meth:`getElementsByTagName` and
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:meth:`getElementsByTagNameNS` methods of :class:`Node` return objects with this
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interface to represent query results.
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The DOM Level 2 recommendation defines one method and one attribute for these
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objects:
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.. method:: NodeList.item(i)
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Return the *i*'th item from the sequence, if there is one, or ``None``. The
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index *i* is not allowed to be less than zero or greater than or equal to the
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length of the sequence.
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.. attribute:: NodeList.length
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The number of nodes in the sequence.
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In addition, the Python DOM interface requires that some additional support is
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provided to allow :class:`NodeList` objects to be used as Python sequences. All
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:class:`NodeList` implementations must include support for
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:meth:`~object.__len__` and
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:meth:`~object.__getitem__`; this allows iteration over the :class:`NodeList` in
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:keyword:`for` statements and proper support for the :func:`len` built-in
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function.
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If a DOM implementation supports modification of the document, the
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:class:`NodeList` implementation must also support the
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:meth:`~object.__setitem__` and :meth:`~object.__delitem__` methods.
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.. _dom-documenttype-objects:
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DocumentType Objects
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^^^^^^^^^^^^^^^^^^^^
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Information about the notations and entities declared by a document (including
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the external subset if the parser uses it and can provide the information) is
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available from a :class:`DocumentType` object. The :class:`DocumentType` for a
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document is available from the :class:`Document` object's :attr:`doctype`
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attribute; if there is no ``DOCTYPE`` declaration for the document, the
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document's :attr:`doctype` attribute will be set to ``None`` instead of an
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instance of this interface.
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:class:`DocumentType` is a specialization of :class:`Node`, and adds the
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following attributes:
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.. attribute:: DocumentType.publicId
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The public identifier for the external subset of the document type definition.
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This will be a string or ``None``.
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.. attribute:: DocumentType.systemId
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The system identifier for the external subset of the document type definition.
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This will be a URI as a string, or ``None``.
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.. attribute:: DocumentType.internalSubset
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A string giving the complete internal subset from the document. This does not
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include the brackets which enclose the subset. If the document has no internal
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subset, this should be ``None``.
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.. attribute:: DocumentType.name
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The name of the root element as given in the ``DOCTYPE`` declaration, if
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present.
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.. attribute:: DocumentType.entities
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This is a :class:`NamedNodeMap` giving the definitions of external entities.
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For entity names defined more than once, only the first definition is provided
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(others are ignored as required by the XML recommendation). This may be
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``None`` if the information is not provided by the parser, or if no entities are
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defined.
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.. attribute:: DocumentType.notations
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This is a :class:`NamedNodeMap` giving the definitions of notations. For
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notation names defined more than once, only the first definition is provided
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(others are ignored as required by the XML recommendation). This may be
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``None`` if the information is not provided by the parser, or if no notations
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are defined.
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|
|
.. _dom-document-objects:
|
|
|
|
Document Objects
|
|
^^^^^^^^^^^^^^^^
|
|
|
|
A :class:`Document` represents an entire XML document, including its constituent
|
|
elements, attributes, processing instructions, comments etc. Remember that it
|
|
inherits properties from :class:`Node`.
|
|
|
|
|
|
.. attribute:: Document.documentElement
|
|
|
|
The one and only root element of the document.
|
|
|
|
|
|
.. method:: Document.createElement(tagName)
|
|
|
|
Create and return a new element node. The element is not inserted into the
|
|
document when it is created. You need to explicitly insert it with one of the
|
|
other methods such as :meth:`insertBefore` or :meth:`appendChild`.
|
|
|
|
|
|
.. method:: Document.createElementNS(namespaceURI, tagName)
|
|
|
|
Create and return a new element with a namespace. The *tagName* may have a
|
|
prefix. The element is not inserted into the document when it is created. You
|
|
need to explicitly insert it with one of the other methods such as
|
|
:meth:`insertBefore` or :meth:`appendChild`.
|
|
|
|
|
|
.. method:: Document.createTextNode(data)
|
|
|
|
Create and return a text node containing the data passed as a parameter. As
|
|
with the other creation methods, this one does not insert the node into the
|
|
tree.
|
|
|
|
|
|
.. method:: Document.createComment(data)
|
|
|
|
Create and return a comment node containing the data passed as a parameter. As
|
|
with the other creation methods, this one does not insert the node into the
|
|
tree.
|
|
|
|
|
|
.. method:: Document.createProcessingInstruction(target, data)
|
|
|
|
Create and return a processing instruction node containing the *target* and
|
|
*data* passed as parameters. As with the other creation methods, this one does
|
|
not insert the node into the tree.
|
|
|
|
|
|
.. method:: Document.createAttribute(name)
|
|
|
|
Create and return an attribute node. This method does not associate the
|
|
attribute node with any particular element. You must use
|
|
:meth:`setAttributeNode` on the appropriate :class:`Element` object to use the
|
|
newly created attribute instance.
|
|
|
|
|
|
.. method:: Document.createAttributeNS(namespaceURI, qualifiedName)
|
|
|
|
Create and return an attribute node with a namespace. The *tagName* may have a
|
|
prefix. This method does not associate the attribute node with any particular
|
|
element. You must use :meth:`setAttributeNode` on the appropriate
|
|
:class:`Element` object to use the newly created attribute instance.
|
|
|
|
|
|
.. method:: Document.getElementsByTagName(tagName)
|
|
|
|
Search for all descendants (direct children, children's children, etc.) with a
|
|
particular element type name.
|
|
|
|
|
|
.. method:: Document.getElementsByTagNameNS(namespaceURI, localName)
|
|
|
|
Search for all descendants (direct children, children's children, etc.) with a
|
|
particular namespace URI and localname. The localname is the part of the
|
|
namespace after the prefix.
|
|
|
|
|
|
.. _dom-element-objects:
|
|
|
|
Element Objects
|
|
^^^^^^^^^^^^^^^
|
|
|
|
:class:`Element` is a subclass of :class:`Node`, so inherits all the attributes
|
|
of that class.
|
|
|
|
|
|
.. attribute:: Element.tagName
|
|
|
|
The element type name. In a namespace-using document it may have colons in it.
|
|
The value is a string.
|
|
|
|
|
|
.. method:: Element.getElementsByTagName(tagName)
|
|
|
|
Same as equivalent method in the :class:`Document` class.
|
|
|
|
|
|
.. method:: Element.getElementsByTagNameNS(namespaceURI, localName)
|
|
|
|
Same as equivalent method in the :class:`Document` class.
|
|
|
|
|
|
.. method:: Element.hasAttribute(name)
|
|
|
|
Return ``True`` if the element has an attribute named by *name*.
|
|
|
|
|
|
.. method:: Element.hasAttributeNS(namespaceURI, localName)
|
|
|
|
Return ``True`` if the element has an attribute named by *namespaceURI* and
|
|
*localName*.
|
|
|
|
|
|
.. method:: Element.getAttribute(name)
|
|
|
|
Return the value of the attribute named by *name* as a string. If no such
|
|
attribute exists, an empty string is returned, as if the attribute had no value.
|
|
|
|
|
|
.. method:: Element.getAttributeNode(attrname)
|
|
|
|
Return the :class:`Attr` node for the attribute named by *attrname*.
|
|
|
|
|
|
.. method:: Element.getAttributeNS(namespaceURI, localName)
|
|
|
|
Return the value of the attribute named by *namespaceURI* and *localName* as a
|
|
string. If no such attribute exists, an empty string is returned, as if the
|
|
attribute had no value.
|
|
|
|
|
|
.. method:: Element.getAttributeNodeNS(namespaceURI, localName)
|
|
|
|
Return an attribute value as a node, given a *namespaceURI* and *localName*.
|
|
|
|
|
|
.. method:: Element.removeAttribute(name)
|
|
|
|
Remove an attribute by name. If there is no matching attribute, a
|
|
:exc:`NotFoundErr` is raised.
|
|
|
|
|
|
.. method:: Element.removeAttributeNode(oldAttr)
|
|
|
|
Remove and return *oldAttr* from the attribute list, if present. If *oldAttr* is
|
|
not present, :exc:`NotFoundErr` is raised.
|
|
|
|
|
|
.. method:: Element.removeAttributeNS(namespaceURI, localName)
|
|
|
|
Remove an attribute by name. Note that it uses a localName, not a qname. No
|
|
exception is raised if there is no matching attribute.
|
|
|
|
|
|
.. method:: Element.setAttribute(name, value)
|
|
|
|
Set an attribute value from a string.
|
|
|
|
|
|
.. method:: Element.setAttributeNode(newAttr)
|
|
|
|
Add a new attribute node to the element, replacing an existing attribute if
|
|
necessary if the :attr:`name` attribute matches. If a replacement occurs, the
|
|
old attribute node will be returned. If *newAttr* is already in use,
|
|
:exc:`InuseAttributeErr` will be raised.
|
|
|
|
|
|
.. method:: Element.setAttributeNodeNS(newAttr)
|
|
|
|
Add a new attribute node to the element, replacing an existing attribute if
|
|
necessary if the :attr:`namespaceURI` and :attr:`localName` attributes match.
|
|
If a replacement occurs, the old attribute node will be returned. If *newAttr*
|
|
is already in use, :exc:`InuseAttributeErr` will be raised.
|
|
|
|
|
|
.. method:: Element.setAttributeNS(namespaceURI, qname, value)
|
|
|
|
Set an attribute value from a string, given a *namespaceURI* and a *qname*.
|
|
Note that a qname is the whole attribute name. This is different than above.
|
|
|
|
|
|
.. _dom-attr-objects:
|
|
|
|
Attr Objects
|
|
^^^^^^^^^^^^
|
|
|
|
:class:`Attr` inherits from :class:`Node`, so inherits all its attributes.
|
|
|
|
|
|
.. attribute:: Attr.name
|
|
|
|
The attribute name.
|
|
In a namespace-using document it may include a colon.
|
|
|
|
|
|
.. attribute:: Attr.localName
|
|
|
|
The part of the name following the colon if there is one, else the
|
|
entire name.
|
|
This is a read-only attribute.
|
|
|
|
|
|
.. attribute:: Attr.prefix
|
|
|
|
The part of the name preceding the colon if there is one, else the
|
|
empty string.
|
|
|
|
|
|
.. attribute:: Attr.value
|
|
|
|
The text value of the attribute. This is a synonym for the
|
|
:attr:`nodeValue` attribute.
|
|
|
|
|
|
.. _dom-attributelist-objects:
|
|
|
|
NamedNodeMap Objects
|
|
^^^^^^^^^^^^^^^^^^^^
|
|
|
|
:class:`NamedNodeMap` does *not* inherit from :class:`Node`.
|
|
|
|
|
|
.. attribute:: NamedNodeMap.length
|
|
|
|
The length of the attribute list.
|
|
|
|
|
|
.. method:: NamedNodeMap.item(index)
|
|
|
|
Return an attribute with a particular index. The order you get the attributes
|
|
in is arbitrary but will be consistent for the life of a DOM. Each item is an
|
|
attribute node. Get its value with the :attr:`value` attribute.
|
|
|
|
There are also experimental methods that give this class more mapping behavior.
|
|
You can use them or you can use the standardized :meth:`getAttribute\*` family
|
|
of methods on the :class:`Element` objects.
|
|
|
|
|
|
.. _dom-comment-objects:
|
|
|
|
Comment Objects
|
|
^^^^^^^^^^^^^^^
|
|
|
|
:class:`Comment` represents a comment in the XML document. It is a subclass of
|
|
:class:`Node`, but cannot have child nodes.
|
|
|
|
|
|
.. attribute:: Comment.data
|
|
|
|
The content of the comment as a string. The attribute contains all characters
|
|
between the leading ``<!-``\ ``-`` and trailing ``-``\ ``->``, but does not
|
|
include them.
|
|
|
|
|
|
.. _dom-text-objects:
|
|
|
|
Text and CDATASection Objects
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
The :class:`Text` interface represents text in the XML document. If the parser
|
|
and DOM implementation support the DOM's XML extension, portions of the text
|
|
enclosed in CDATA marked sections are stored in :class:`CDATASection` objects.
|
|
These two interfaces are identical, but provide different values for the
|
|
:attr:`nodeType` attribute.
|
|
|
|
These interfaces extend the :class:`Node` interface. They cannot have child
|
|
nodes.
|
|
|
|
|
|
.. attribute:: Text.data
|
|
|
|
The content of the text node as a string.
|
|
|
|
.. note::
|
|
|
|
The use of a :class:`CDATASection` node does not indicate that the node
|
|
represents a complete CDATA marked section, only that the content of the node
|
|
was part of a CDATA section. A single CDATA section may be represented by more
|
|
than one node in the document tree. There is no way to determine whether two
|
|
adjacent :class:`CDATASection` nodes represent different CDATA marked sections.
|
|
|
|
|
|
.. _dom-pi-objects:
|
|
|
|
ProcessingInstruction Objects
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
Represents a processing instruction in the XML document; this inherits from the
|
|
:class:`Node` interface and cannot have child nodes.
|
|
|
|
|
|
.. attribute:: ProcessingInstruction.target
|
|
|
|
The content of the processing instruction up to the first whitespace character.
|
|
This is a read-only attribute.
|
|
|
|
|
|
.. attribute:: ProcessingInstruction.data
|
|
|
|
The content of the processing instruction following the first whitespace
|
|
character.
|
|
|
|
|
|
.. _dom-exceptions:
|
|
|
|
Exceptions
|
|
^^^^^^^^^^
|
|
|
|
The DOM Level 2 recommendation defines a single exception, :exc:`DOMException`,
|
|
and a number of constants that allow applications to determine what sort of
|
|
error occurred. :exc:`DOMException` instances carry a :attr:`code` attribute
|
|
that provides the appropriate value for the specific exception.
|
|
|
|
The Python DOM interface provides the constants, but also expands the set of
|
|
exceptions so that a specific exception exists for each of the exception codes
|
|
defined by the DOM. The implementations must raise the appropriate specific
|
|
exception, each of which carries the appropriate value for the :attr:`code`
|
|
attribute.
|
|
|
|
|
|
.. exception:: DOMException
|
|
|
|
Base exception class used for all specific DOM exceptions. This exception class
|
|
cannot be directly instantiated.
|
|
|
|
|
|
.. exception:: DomstringSizeErr
|
|
|
|
Raised when a specified range of text does not fit into a string. This is not
|
|
known to be used in the Python DOM implementations, but may be received from DOM
|
|
implementations not written in Python.
|
|
|
|
|
|
.. exception:: HierarchyRequestErr
|
|
|
|
Raised when an attempt is made to insert a node where the node type is not
|
|
allowed.
|
|
|
|
|
|
.. exception:: IndexSizeErr
|
|
|
|
Raised when an index or size parameter to a method is negative or exceeds the
|
|
allowed values.
|
|
|
|
|
|
.. exception:: InuseAttributeErr
|
|
|
|
Raised when an attempt is made to insert an :class:`Attr` node that is already
|
|
present elsewhere in the document.
|
|
|
|
|
|
.. exception:: InvalidAccessErr
|
|
|
|
Raised if a parameter or an operation is not supported on the underlying object.
|
|
|
|
|
|
.. exception:: InvalidCharacterErr
|
|
|
|
This exception is raised when a string parameter contains a character that is
|
|
not permitted in the context it's being used in by the XML 1.0 recommendation.
|
|
For example, attempting to create an :class:`Element` node with a space in the
|
|
element type name will cause this error to be raised.
|
|
|
|
|
|
.. exception:: InvalidModificationErr
|
|
|
|
Raised when an attempt is made to modify the type of a node.
|
|
|
|
|
|
.. exception:: InvalidStateErr
|
|
|
|
Raised when an attempt is made to use an object that is not defined or is no
|
|
longer usable.
|
|
|
|
|
|
.. exception:: NamespaceErr
|
|
|
|
If an attempt is made to change any object in a way that is not permitted with
|
|
regard to the `Namespaces in XML <https://www.w3.org/TR/REC-xml-names/>`_
|
|
recommendation, this exception is raised.
|
|
|
|
|
|
.. exception:: NotFoundErr
|
|
|
|
Exception when a node does not exist in the referenced context. For example,
|
|
:meth:`NamedNodeMap.removeNamedItem` will raise this if the node passed in does
|
|
not exist in the map.
|
|
|
|
|
|
.. exception:: NotSupportedErr
|
|
|
|
Raised when the implementation does not support the requested type of object or
|
|
operation.
|
|
|
|
|
|
.. exception:: NoDataAllowedErr
|
|
|
|
This is raised if data is specified for a node which does not support data.
|
|
|
|
.. XXX a better explanation is needed!
|
|
|
|
|
|
.. exception:: NoModificationAllowedErr
|
|
|
|
Raised on attempts to modify an object where modifications are not allowed (such
|
|
as for read-only nodes).
|
|
|
|
|
|
.. exception:: SyntaxErr
|
|
|
|
Raised when an invalid or illegal string is specified.
|
|
|
|
.. XXX how is this different from InvalidCharacterErr?
|
|
|
|
|
|
.. exception:: WrongDocumentErr
|
|
|
|
Raised when a node is inserted in a different document than it currently belongs
|
|
to, and the implementation does not support migrating the node from one document
|
|
to the other.
|
|
|
|
The exception codes defined in the DOM recommendation map to the exceptions
|
|
described above according to this table:
|
|
|
|
+--------------------------------------+---------------------------------+
|
|
| Constant | Exception |
|
|
+======================================+=================================+
|
|
| :const:`DOMSTRING_SIZE_ERR` | :exc:`DomstringSizeErr` |
|
|
+--------------------------------------+---------------------------------+
|
|
| :const:`HIERARCHY_REQUEST_ERR` | :exc:`HierarchyRequestErr` |
|
|
+--------------------------------------+---------------------------------+
|
|
| :const:`INDEX_SIZE_ERR` | :exc:`IndexSizeErr` |
|
|
+--------------------------------------+---------------------------------+
|
|
| :const:`INUSE_ATTRIBUTE_ERR` | :exc:`InuseAttributeErr` |
|
|
+--------------------------------------+---------------------------------+
|
|
| :const:`INVALID_ACCESS_ERR` | :exc:`InvalidAccessErr` |
|
|
+--------------------------------------+---------------------------------+
|
|
| :const:`INVALID_CHARACTER_ERR` | :exc:`InvalidCharacterErr` |
|
|
+--------------------------------------+---------------------------------+
|
|
| :const:`INVALID_MODIFICATION_ERR` | :exc:`InvalidModificationErr` |
|
|
+--------------------------------------+---------------------------------+
|
|
| :const:`INVALID_STATE_ERR` | :exc:`InvalidStateErr` |
|
|
+--------------------------------------+---------------------------------+
|
|
| :const:`NAMESPACE_ERR` | :exc:`NamespaceErr` |
|
|
+--------------------------------------+---------------------------------+
|
|
| :const:`NOT_FOUND_ERR` | :exc:`NotFoundErr` |
|
|
+--------------------------------------+---------------------------------+
|
|
| :const:`NOT_SUPPORTED_ERR` | :exc:`NotSupportedErr` |
|
|
+--------------------------------------+---------------------------------+
|
|
| :const:`NO_DATA_ALLOWED_ERR` | :exc:`NoDataAllowedErr` |
|
|
+--------------------------------------+---------------------------------+
|
|
| :const:`NO_MODIFICATION_ALLOWED_ERR` | :exc:`NoModificationAllowedErr` |
|
|
+--------------------------------------+---------------------------------+
|
|
| :const:`SYNTAX_ERR` | :exc:`SyntaxErr` |
|
|
+--------------------------------------+---------------------------------+
|
|
| :const:`WRONG_DOCUMENT_ERR` | :exc:`WrongDocumentErr` |
|
|
+--------------------------------------+---------------------------------+
|
|
|
|
|
|
.. _dom-conformance:
|
|
|
|
Conformance
|
|
-----------
|
|
|
|
This section describes the conformance requirements and relationships between
|
|
the Python DOM API, the W3C DOM recommendations, and the OMG IDL mapping for
|
|
Python.
|
|
|
|
|
|
.. _dom-type-mapping:
|
|
|
|
Type Mapping
|
|
^^^^^^^^^^^^
|
|
|
|
The IDL types used in the DOM specification are mapped to Python types
|
|
according to the following table.
|
|
|
|
+------------------+-------------------------------------------+
|
|
| IDL Type | Python Type |
|
|
+==================+===========================================+
|
|
| ``boolean`` | ``bool`` or ``int`` |
|
|
+------------------+-------------------------------------------+
|
|
| ``int`` | ``int`` |
|
|
+------------------+-------------------------------------------+
|
|
| ``long int`` | ``int`` |
|
|
+------------------+-------------------------------------------+
|
|
| ``unsigned int`` | ``int`` |
|
|
+------------------+-------------------------------------------+
|
|
| ``DOMString`` | ``str`` or ``bytes`` |
|
|
+------------------+-------------------------------------------+
|
|
| ``null`` | ``None`` |
|
|
+------------------+-------------------------------------------+
|
|
|
|
.. _dom-accessor-methods:
|
|
|
|
Accessor Methods
|
|
^^^^^^^^^^^^^^^^
|
|
|
|
The mapping from OMG IDL to Python defines accessor functions for IDL
|
|
``attribute`` declarations in much the way the Java mapping does.
|
|
Mapping the IDL declarations ::
|
|
|
|
readonly attribute string someValue;
|
|
attribute string anotherValue;
|
|
|
|
yields three accessor functions: a "get" method for :attr:`someValue`
|
|
(:meth:`_get_someValue`), and "get" and "set" methods for :attr:`anotherValue`
|
|
(:meth:`_get_anotherValue` and :meth:`_set_anotherValue`). The mapping, in
|
|
particular, does not require that the IDL attributes are accessible as normal
|
|
Python attributes: ``object.someValue`` is *not* required to work, and may
|
|
raise an :exc:`AttributeError`.
|
|
|
|
The Python DOM API, however, *does* require that normal attribute access work.
|
|
This means that the typical surrogates generated by Python IDL compilers are not
|
|
likely to work, and wrapper objects may be needed on the client if the DOM
|
|
objects are accessed via CORBA. While this does require some additional
|
|
consideration for CORBA DOM clients, the implementers with experience using DOM
|
|
over CORBA from Python do not consider this a problem. Attributes that are
|
|
declared ``readonly`` may not restrict write access in all DOM
|
|
implementations.
|
|
|
|
In the Python DOM API, accessor functions are not required. If provided, they
|
|
should take the form defined by the Python IDL mapping, but these methods are
|
|
considered unnecessary since the attributes are accessible directly from Python.
|
|
"Set" accessors should never be provided for ``readonly`` attributes.
|
|
|
|
The IDL definitions do not fully embody the requirements of the W3C DOM API,
|
|
such as the notion of certain objects, such as the return value of
|
|
:meth:`getElementsByTagName`, being "live". The Python DOM API does not require
|
|
implementations to enforce such requirements.
|
|
|