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. It then gives access to the structure through a set of objects which provided well-known interfaces.
The DOM is extremely useful for random-access applications. SAX only allows you a view of one bit of the document at a time. If you are looking at one SAX element, you have no access to another. If you are looking at a text node, you have no access to a containing element. When you write a SAX application, you need to keep track of your program’s position in the document somewhere in your own code. SAX does not do it for you. Also, if you need to look ahead in the XML document, you are just out of luck.
Some applications are simply impossible in an event driven model with no access to 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 tree representation for XML data.
The Document Object Model is being defined by the W3C in stages, or “levels” in their terminology. The Python mapping of the API is substantially based on the DOM Level 2 recommendation.
DOM applications typically start by parsing some XML into a DOM. How this is
accomplished is not covered at all by DOM Level 1, and Level 2 provides only
limited improvements: There is a DOMImplementation object class which
provides access to Document creation methods, but no way to access an
XML reader/parser/Document builder in an implementation-independent way. There
is also no well-defined way to access these methods without an existing
Document object. In Python, each DOM implementation will provide a
function getDOMImplementation(). DOM Level 3 adds a Load/Store
specification, which defines an interface to the reader, but this is not yet
available in the Python standard library.
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; this portion of the reference manual describes the interpretation 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 IDL version of the specification, but strict compliance is not required (though implementations are free to support the strict mapping from IDL). See section Conformance for a detailed discussion of mapping requirements.
See also
- Document Object Model (DOM) Level 2 Specification
- The W3C recommendation upon which the Python DOM API is based.
- Document Object Model (DOM) Level 1 Specification
- The W3C recommendation for the DOM supported by
xml.dom.minidom. - Python Language Mapping Specification
- This specifies the mapping from OMG IDL to Python.
19.6.1. Module Contents¶
The xml.dom contains the following functions:
-
xml.dom.registerDOMImplementation(name, factory)¶ Register the factory function with the name name. The factory function should return an object which implements the
DOMImplementationinterface. The factory function can return the same object every time, or a new one for each call, as appropriate for the specific implementation (e.g. if that implementation supports some customization).
-
xml.dom.getDOMImplementation([name[, features]])¶ Return a suitable DOM implementation. The name is either well-known, the module name of a DOM implementation, or
None. If it is notNone, imports the corresponding module and returns aDOMImplementationobject if the import succeeds. If no name is given, and if the environment variablePYTHON_DOMis set, this variable is used to find the implementation.If name is not given, this examines the available implementations to find one with the required feature set. If no implementation can be found, raise an
ImportError. The features list must be a sequence of(feature, version)pairs which are passed to thehasFeature()method on availableDOMImplementationobjects.
Some convenience constants are also provided:
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xml.dom.EMPTY_NAMESPACE¶ The value used to indicate that no namespace is associated with a node in the DOM. This is typically found as the
namespaceURIof a node, or used as the namespaceURI parameter to a namespaces-specific method.New in version 2.2:
New in version 2.2.
-
xml.dom.XML_NAMESPACE¶ The namespace URI associated with the reserved prefix
xml, as defined by Namespaces in XML (section 4).New in version 2.2:
New in version 2.2.