xml.dom — The Document Object Model API (2024)

Source code: Lib/xml/dom/__init__.py

The Document Object Model, or “DOM,” is a cross-language API from the World WideWeb Consortium (W3C) for accessing and modifying XML documents. A DOMimplementation presents an XML document as a tree structure, or allows clientcode to build such a structure from scratch. It then gives access to thestructure through a set of objects which provided well-known interfaces.

The DOM is extremely useful for random-access applications. SAX only allows youa view of one bit of the document at a time. If you are looking at one SAXelement, you have no access to another. If you are looking at a text node, youhave no access to a containing element. When you write a SAX application, youneed to keep track of your program’s position in the document somewhere in yourown code. SAX does not do it for you. Also, if you need to look ahead in theXML document, you are just out of luck.

Some applications are simply impossible in an event driven model with no accessto a tree. Of course you could build some sort of tree yourself in SAX events,but the DOM allows you to avoid writing that code. The DOM is a standard treerepresentation for XML data.

The Document Object Model is being defined by the W3C in stages, or “levels” intheir terminology. The Python mapping of the API is substantially based on theDOM Level 2 recommendation.

DOM applications typically start by parsing some XML into a DOM. How this isaccomplished is not covered at all by DOM Level 1, and Level 2 provides onlylimited improvements: There is a DOMImplementation object class whichprovides access to Document creation methods, but no way to access anXML reader/parser/Document builder in an implementation-independent way. Thereis also no well-defined way to access these methods without an existingDocument object. In Python, each DOM implementation will provide afunction getDOMImplementation(). DOM Level 3 adds a Load/Storespecification, which defines an interface to the reader, but this is not yetavailable in the Python standard library.

Once you have a DOM document object, you can access the parts of your XMLdocument through its properties and methods. These properties are defined inthe DOM specification; this portion of the reference manual describes theinterpretation of the specification in Python.

The specification provided by the W3C defines the DOM API for Java, ECMAScript,and OMG IDL. The Python mapping defined here is based in large part on the IDLversion of the specification, but strict compliance is not required (thoughimplementations are free to support the strict mapping from IDL). See sectionConformance for a detailed discussion of mapping requirements.

Module Contents¶

The xml.dom contains the following functions:

xml.dom.registerDOMImplementation(name, factory)¶: Register the factory function with the name name. The factory functionshould return an object which implements the DOMImplementationinterface. The factory function can return the same object every time, or a newone for each call, as appropriate for the specific implementation (e.g. if thatimplementation supports some customization).

xml.dom.getDOMImplementation(name=None, features=())¶

Return a suitable DOM implementation. The name is either well-known, themodule name of a DOM implementation, or None. If it is not None, importsthe corresponding module and returns a DOMImplementation object if theimport succeeds. If no name is given, and if the environment variablePYTHON_DOM is set, this variable is used to find the implementation.

If name is not given, this examines the available implementations to find onewith the required feature set. If no implementation can be found, raise anImportError. The features list must be a sequence of (feature,version) pairs which are passed to the hasFeature() method on availableDOMImplementation objects.

Some convenience constants are also provided:

xml.dom.EMPTY_NAMESPACE¶: The value used to indicate that no namespace is associated with a node in theDOM. This is typically found as the namespaceURI of a node, or used asthe namespaceURI parameter to a namespaces-specific method.

xml.dom.XML_NAMESPACE¶: The namespace URI associated with the reserved prefix xml, as defined byNamespaces in XML (section 4).

xml.dom.XMLNS_NAMESPACE¶: The namespace URI for namespace declarations, as defined by Document ObjectModel (DOM) Level 2 Core Specification (section 1.1.8).

xml.dom.XHTML_NAMESPACE¶: The URI of the XHTML namespace as defined by XHTML 1.0: The ExtensibleHyperText Markup Language (section 3.1.1).

In addition, xml.dom contains a base Node class and the DOMexception classes. The Node class provided by this module does notimplement any of the methods or attributes defined by the DOM specification;concrete DOM implementations must provide those. The Node classprovided as part of this module does provide the constants used for thenodeType attribute on concrete Node objects; they are locatedwithin the class rather than at the module level to conform with the DOMspecifications.

Objects in the DOM¶

The definitive documentation for the DOM is the DOM specification from the W3C.

Note that DOM attributes may also be manipulated as nodes instead of as simplestrings. It is fairly rare that you must do this, however, so this usage is notyet documented.

Interface	Section	Purpose
`DOMImplementation`	DOMImplementation Objects	Interface to the underlyingimplementation.
`Node`	Node Objects	Base interface for most objectsin a document.
`NodeList`	NodeList Objects	Interface for a sequence ofnodes.
`DocumentType`	DocumentType Objects	Information about thedeclarations needed to processa document.
`Document`	Document Objects	Object which represents anentire document.
`Element`	Element Objects	Element nodes in the documenthierarchy.
`Attr`	Attr Objects	Attribute value nodes onelement nodes.
`Comment`	Comment Objects	Representation of comments inthe source document.
`Text`	Text and CDATASection Objects	Nodes containing textualcontent from the document.
`ProcessingInstruction`	ProcessingInstruction Objects	Processing instructionrepresentation.

An additional section describes the exceptions defined for working with the DOMin Python.

DOMImplementation Objects¶

The DOMImplementation interface provides a way for applications todetermine the availability of particular features in the DOM they are using.DOM Level 2 added the ability to create new Document andDocumentType objects using the DOMImplementation as well.

DOMImplementation.hasFeature(feature, version)¶: Return True if the feature identified by the pair of strings feature andversion is implemented.

DOMImplementation.createDocument(namespaceUri, qualifiedName, doctype)¶: Return a new Document object (the root of the DOM), with a childElement object having the given namespaceUri and qualifiedName. Thedoctype must be a DocumentType object created bycreateDocumentType(), or None. In the Python DOM API, the first twoarguments can also be None in order to indicate that no Elementchild is to be created.

DOMImplementation.createDocumentType(qualifiedName, publicId, systemId)¶: Return a new DocumentType object that encapsulates the givenqualifiedName, publicId, and systemId strings, representing theinformation contained in an XML document type declaration.

Node Objects¶

All of the components of an XML document are subclasses of Node.

Node.nodeType¶: An integer representing the node type. Symbolic constants for the types are onthe Node object: ELEMENT_NODE, ATTRIBUTE_NODE,TEXT_NODE, CDATA_SECTION_NODE, ENTITY_NODE,PROCESSING_INSTRUCTION_NODE, COMMENT_NODE,DOCUMENT_NODE, DOCUMENT_TYPE_NODE, NOTATION_NODE.This is a read-only attribute.

Node.parentNode¶: The parent of the current node, or None for the document node. The value isalways a Node object or None. For Element nodes, thiswill be the parent element, except for the root element, in which case it willbe the Document object. For Attr nodes, this is alwaysNone. This is a read-only attribute.

Node.attributes¶: A NamedNodeMap of attribute objects. Only elements have actual valuesfor this; others provide None for this attribute. This is a read-onlyattribute.

Node.previousSibling¶

The node that immediately precedes this one with the same parent. Forinstance the element with an end-tag that comes just before the selfelement’s start-tag. Of course, XML documents are made up of more than justelements so the previous sibling could be text, a comment, or something else.If this node is the first child of the parent, this attribute will beNone. This is a read-only attribute.

NodeList Objects¶

A NodeList represents a sequence of nodes. These objects are used intwo ways in the DOM Core recommendation: an Element object providesone as its list of child nodes, and the getElementsByTagName() andgetElementsByTagNameNS() methods of Node return objects with thisinterface to represent query results.

The DOM Level 2 recommendation defines one method and one attribute for theseobjects:

NodeList.item(i)¶: Return the i’th item from the sequence, if there is one, or None. Theindex i is not allowed to be less than zero or greater than or equal to thelength of the sequence.

NodeList.length¶: The number of nodes in the sequence.

In addition, the Python DOM interface requires that some additional support isprovided to allow NodeList objects to be used as Python sequences. AllNodeList implementations must include support for__len__() and__getitem__(); this allows iteration over the NodeList infor statements and proper support for the len() built-infunction.

If a DOM implementation supports modification of the document, theNodeList implementation must also support the__setitem__() and __delitem__() methods.

DocumentType Objects¶

Information about the notations and entities declared by a document (includingthe external subset if the parser uses it and can provide the information) isavailable from a DocumentType object. The DocumentType for adocument is available from the Document object’s doctypeattribute; if there is no DOCTYPE declaration for the document, thedocument’s doctype attribute will be set to None instead of aninstance of this interface.

DocumentType is a specialization of Node, and adds thefollowing attributes:

DocumentType.publicId¶: The public identifier for the external subset of the document type definition.This will be a string or None.

DocumentType.systemId¶: The system identifier for the external subset of the document type definition.This will be a URI as a string, or None.

DocumentType.internalSubset¶: A string giving the complete internal subset from the document. This does notinclude the brackets which enclose the subset. If the document has no internalsubset, this should be None.

DocumentType.name¶: The name of the root element as given in the DOCTYPE declaration, ifpresent.

DocumentType.entities¶: This is a NamedNodeMap giving the definitions of external entities.For entity names defined more than once, only the first definition is provided(others are ignored as required by the XML recommendation). This may beNone if the information is not provided by the parser, or if no entities aredefined.

DocumentType.notations¶: This is a NamedNodeMap giving the definitions of notations. Fornotation names defined more than once, only the first definition is provided(others are ignored as required by the XML recommendation). This may beNone if the information is not provided by the parser, or if no notationsare defined.

Document Objects¶

A Document represents an entire XML document, including its constituentelements, attributes, processing instructions, comments etc. Remember that itinherits properties from Node.

Document.documentElement¶: The one and only root element of the document.

Document.createElement(tagName)¶: Create and return a new element node. The element is not inserted into thedocument when it is created. You need to explicitly insert it with one of theother methods such as insertBefore() or appendChild().

Document.createElementNS(namespaceURI, tagName)¶: Create and return a new element with a namespace. The tagName may have aprefix. The element is not inserted into the document when it is created. Youneed to explicitly insert it with one of the other methods such asinsertBefore() or appendChild().

Document.createTextNode(data)¶: Create and return a text node containing the data passed as a parameter. Aswith the other creation methods, this one does not insert the node into thetree.

Document.createComment(data)¶: Create and return a comment node containing the data passed as a parameter. Aswith the other creation methods, this one does not insert the node into thetree.

Document.createProcessingInstruction(target, data)¶: Create and return a processing instruction node containing the target anddata passed as parameters. As with the other creation methods, this one doesnot insert the node into the tree.

Document.createAttribute(name)¶: Create and return an attribute node. This method does not associate theattribute node with any particular element. You must usesetAttributeNode() on the appropriate Element object to use thenewly created attribute instance.

Document.createAttributeNS(namespaceURI, qualifiedName)¶: Create and return an attribute node with a namespace. The tagName may have aprefix. This method does not associate the attribute node with any particularelement. You must use setAttributeNode() on the appropriateElement object to use the newly created attribute instance.

Document.getElementsByTagName(tagName)¶: Search for all descendants (direct children, children’s children, etc.) with aparticular element type name.

Document.getElementsByTagNameNS(namespaceURI, localName)¶: Search for all descendants (direct children, children’s children, etc.) with aparticular namespace URI and localname. The localname is the part of thenamespace after the prefix.

Element Objects¶

Element is a subclass of Node, so inherits all the attributesof that class.

Element.tagName¶: The element type name. In a namespace-using document it may have colons in it.The value is a string.

Element.getElementsByTagName(tagName)¶: Same as equivalent method in the Document class.

Element.getElementsByTagNameNS(namespaceURI, localName)¶: Same as equivalent method in the Document class.

Element.hasAttribute(name)¶: Return True if the element has an attribute named by name.

Element.hasAttributeNS(namespaceURI, localName)¶: Return True if the element has an attribute named by namespaceURI andlocalName.

Element.getAttribute(name)¶: Return the value of the attribute named by name as a string. If no suchattribute exists, an empty string is returned, as if the attribute had no value.

Element.getAttributeNode(attrname)¶: Return the Attr node for the attribute named by attrname.

Element.getAttributeNS(namespaceURI, localName)¶: Return the value of the attribute named by namespaceURI and localName as astring. If no such attribute exists, an empty string is returned, as if theattribute had no value.

Element.getAttributeNodeNS(namespaceURI, localName)¶: Return an attribute value as a node, given a namespaceURI and localName.

Element.removeAttribute(name)¶: Remove an attribute by name. If there is no matching attribute, aNotFoundErr is raised.

Element.removeAttributeNode(oldAttr)¶: Remove and return oldAttr from the attribute list, if present. If oldAttr isnot present, NotFoundErr is raised.

Element.removeAttributeNS(namespaceURI, localName)¶: Remove an attribute by name. Note that it uses a localName, not a qname. Noexception is raised if there is no matching attribute.

Element.setAttribute(name, value)¶: Set an attribute value from a string.

Element.setAttributeNode(newAttr)¶: Add a new attribute node to the element, replacing an existing attribute ifnecessary if the name attribute matches. If a replacement occurs, theold attribute node will be returned. If newAttr is already in use,InuseAttributeErr will be raised.

Element.setAttributeNodeNS(newAttr)¶: Add a new attribute node to the element, replacing an existing attribute ifnecessary if the namespaceURI and localName attributes match.If a replacement occurs, the old attribute node will be returned. If newAttris already in use, InuseAttributeErr will be raised.

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.

Attr Objects¶

Attr inherits from Node, so inherits all its attributes.

Attr.name¶: The attribute name.In a namespace-using document it may include a colon.

Attr.localName¶: The part of the name following the colon if there is one, else theentire name.This is a read-only attribute.

Attr.prefix¶: The part of the name preceding the colon if there is one, else theempty string.

Attr.value¶: The text value of the attribute. This is a synonym for thenodeValue attribute.

NamedNodeMap Objects¶

NamedNodeMap does not inherit from Node.

NamedNodeMap.length¶: The length of the attribute list.

NamedNodeMap.item(index)¶: Return an attribute with a particular index. The order you get the attributesin is arbitrary but will be consistent for the life of a DOM. Each item is anattribute node. Get its value with the value attribute.

There are also experimental methods that give this class more mapping behavior.You can use them or you can use the standardized getAttribute*() familyof methods on the Element objects.

Comment Objects¶

Comment represents a comment in the XML document. It is a subclass ofNode, but cannot have child nodes.

Comment.data¶: The content of the comment as a string. The attribute contains all charactersbetween the leading , but does notinclude them.

Text and CDATASection Objects¶

The Text interface represents text in the XML document. If the parserand DOM implementation support the DOM’s XML extension, portions of the textenclosed in CDATA marked sections are stored in CDATASection objects.These two interfaces are identical, but provide different values for thenodeType attribute.

These interfaces extend the Node interface. They cannot have childnodes.

Text.data¶: The content of the text node as a string.

Note

The use of a CDATASection node does not indicate that the noderepresents a complete CDATA marked section, only that the content of the nodewas part of a CDATA section. A single CDATA section may be represented by morethan one node in the document tree. There is no way to determine whether twoadjacent CDATASection nodes represent different CDATA marked sections.

ProcessingInstruction Objects¶

Represents a processing instruction in the XML document; this inherits from theNode interface and cannot have child nodes.

ProcessingInstruction.target¶: The content of the processing instruction up to the first whitespace character.This is a read-only attribute.

ProcessingInstruction.data¶: The content of the processing instruction following the first whitespacecharacter.

Exceptions¶

The DOM Level 2 recommendation defines a single exception, DOMException,and a number of constants that allow applications to determine what sort oferror occurred. DOMException instances carry a code attributethat provides the appropriate value for the specific exception.

The Python DOM interface provides the constants, but also expands the set ofexceptions so that a specific exception exists for each of the exception codesdefined by the DOM. The implementations must raise the appropriate specificexception, each of which carries the appropriate value for the codeattribute.

exception xml.dom.DOMException¶: Base exception class used for all specific DOM exceptions. This exception classcannot be directly instantiated.

exception xml.dom.DomstringSizeErr¶: Raised when a specified range of text does not fit into a string. This is notknown to be used in the Python DOM implementations, but may be received from DOMimplementations not written in Python.

exception xml.dom.HierarchyRequestErr¶: Raised when an attempt is made to insert a node where the node type is notallowed.

exception xml.dom.IndexSizeErr¶: Raised when an index or size parameter to a method is negative or exceeds theallowed values.

exception xml.dom.InuseAttributeErr¶: Raised when an attempt is made to insert an Attr node that is alreadypresent elsewhere in the document.

exception xml.dom.InvalidAccessErr¶: Raised if a parameter or an operation is not supported on the underlying object.

exception xml.dom.InvalidCharacterErr¶: This exception is raised when a string parameter contains a character that isnot permitted in the context it’s being used in by the XML 1.0 recommendation.For example, attempting to create an Element node with a space in theelement type name will cause this error to be raised.

exception xml.dom.InvalidModificationErr¶: Raised when an attempt is made to modify the type of a node.

exception xml.dom.InvalidStateErr¶: Raised when an attempt is made to use an object that is not defined or is nolonger usable.

exception xml.dom.NamespaceErr¶: If an attempt is made to change any object in a way that is not permitted withregard to the Namespaces in XMLrecommendation, this exception is raised.

exception xml.dom.NotFoundErr¶: Exception when a node does not exist in the referenced context. For example,NamedNodeMap.removeNamedItem() will raise this if the node passed in doesnot exist in the map.

exception xml.dom.NotSupportedErr¶: Raised when the implementation does not support the requested type of object oroperation.

exception xml.dom.NoDataAllowedErr¶: This is raised if data is specified for a node which does not support data.

exception xml.dom.NoModificationAllowedErr¶: Raised on attempts to modify an object where modifications are not allowed (suchas for read-only nodes).

exception xml.dom.SyntaxErr¶: Raised when an invalid or illegal string is specified.

exception xml.dom.WrongDocumentErr¶: Raised when a node is inserted in a different document than it currently belongsto, and the implementation does not support migrating the node from one documentto the other.

The exception codes defined in the DOM recommendation map to the exceptionsdescribed above according to this table:

Constant	Exception
`DOMSTRING_SIZE_ERR`	DomstringSizeErr
`HIERARCHY_REQUEST_ERR`	HierarchyRequestErr
`INDEX_SIZE_ERR`	IndexSizeErr
`INUSE_ATTRIBUTE_ERR`	InuseAttributeErr
`INVALID_ACCESS_ERR`	InvalidAccessErr
`INVALID_CHARACTER_ERR`	InvalidCharacterErr
`INVALID_MODIFICATION_ERR`	InvalidModificationErr
`INVALID_STATE_ERR`	InvalidStateErr
`NAMESPACE_ERR`	NamespaceErr
`NOT_FOUND_ERR`	NotFoundErr
`NOT_SUPPORTED_ERR`	NotSupportedErr
`NO_DATA_ALLOWED_ERR`	NoDataAllowedErr
`NO_MODIFICATION_ALLOWED_ERR`	NoModificationAllowedErr
`SYNTAX_ERR`	SyntaxErr
`WRONG_DOCUMENT_ERR`	WrongDocumentErr

Conformance¶

This section describes the conformance requirements and relationships betweenthe Python DOM API, the W3C DOM recommendations, and the OMG IDL mapping forPython.

Type Mapping¶

The IDL types used in the DOM specification are mapped to Python typesaccording 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`

Accessor Methods¶

The mapping from OMG IDL to Python defines accessor functions for IDLattribute 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 someValue(_get_someValue()), and “get” and “set” methods for anotherValue(_get_anotherValue() and _set_anotherValue()). The mapping, inparticular, does not require that the IDL attributes are accessible as normalPython attributes: object.someValue is not required to work, and mayraise an 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 notlikely to work, and wrapper objects may be needed on the client if the DOMobjects are accessed via CORBA. While this does require some additionalconsideration for CORBA DOM clients, the implementers with experience using DOMover CORBA from Python do not consider this a problem. Attributes that aredeclared readonly may not restrict write access in all DOMimplementations.

In the Python DOM API, accessor functions are not required. If provided, theyshould take the form defined by the Python IDL mapping, but these methods areconsidered 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 ofgetElementsByTagName(), being “live”. The Python DOM API does not requireimplementations to enforce such requirements.

FAQs

Xml.dom — The Document Object Model API? ›

dom — The Document Object Model API. The Document Object Model, or “DOM,” is a cross-language API from the World Wide Web Consortium (W3C) for accessing and modifying XML documents. A DOM implementation presents an XML document as a tree structure, or allows client code to build such a structure from scratch.

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What is XML DOM document object model? ›

The XML Document Object Model (DOM) class is an in-memory representation of an XML document. The DOM allows you to programmatically read, manipulate, and modify an XML document. The XmlReader class also reads XML; however, it provides non-cached, forward-only, read-only access.

Is the Document Object Model or DOM a web api? ›

The Document Object Model (DOM) is an application programming interface (API) for HTML and XML documents. It defines the logical structure of documents and the way a document is accessed and manipulated.

Can you use Python for DOM? ›

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.

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What does DOM mean Python? ›

The DOM (document object model) is a tree like data structure representing the web page displayed by the browser. PyScript interacts with the DOM to change the user interface and react to things happening in the browser.

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What is API function in Python? ›

As you are likely aware, API stands for Application Programming Interface. At its core, an API is a set of rules that allows different software applications to communicate with each other. It's a bridge between different software systems, enabling them to interact and exchange data in a structured and secure manner.

What is the difference between DOM and XML DOM? ›

The HTML DOM defines a standard way for accessing and manipulating HTML documents. It presents an HTML document as a tree-structure. The XML DOM defines a standard way for accessing and manipulating XML documents. It presents an XML document as a tree-structure.

What is XSL and how does it work? ›

XSL (eXtensible Stylesheet Language) is a styling language for XML. XSLT stands for XSL Transformations. This tutorial will teach you how to use XSLT to transform XML documents into other formats (like transforming XML into HTML).

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What is DOM data object model? ›

The Document Object Model (DOM) is a cross-platform and language-independent interface that treats an HTML or XML document as a tree structure wherein each node is an object representing a part of the document. The DOM represents a document with a logical tree.

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What is the difference between DOM and document object? ›

So basically Document Object Model is an API that represents and interacts with HTML or XML documents. The DOM is a W3C (World Wide Web Consortium) standard and it defines a standard for accessing documents. The W3C Dom standard is divided into three different parts: Core DOM – standard model for all document types.

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