xml.dom.pulldom — Support for building partial DOM trees

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

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The xml.dom.pulldom module provides a «pull parser» which can also be asked to produce DOM-accessible fragments of the document where necessary. The basic concept involves pulling «events» from a stream of incoming XML and processing them. In contrast to SAX which also employs an event-driven processing model together with callbacks, the user of a pull parser is responsible for explicitly pulling events from the stream, looping over those events until either processing is finished or an error condition occurs.

Nota

If you need to parse untrusted or unauthenticated data, see XML security.

Distinto en la versión 3.7.1: El analizador SAX ya no procesa entidades externas generales de forma predeterminada para aumentar la seguridad de forma predeterminada. Para habilitar el procesamiento de entidades externas, pase una instancia de analizador personalizada (custom parser instance in::)

from xml.dom.pulldom import parse
from xml.sax import make_parser
from xml.sax.handler import feature_external_ges

parser = make_parser()
parser.setFeature(feature_external_ges, True)
parse(filename, parser=parser)

Ejemplo:

from xml.dom import pulldom

doc = pulldom.parse('sales_items.xml')
for event, node in doc:
    if event == pulldom.START_ELEMENT and node.tagName == 'item':
        if int(node.getAttribute('price')) > 50:
            doc.expandNode(node)
            print(node.toxml())

event is one of the following constants, and node is the node which the event is about. The nodes implement the xml.dom interfaces; they are created by the DOM implementation given to PullDOM, which is xml.dom.minidom by default.

xml.dom.pulldom.START_DOCUMENT

xml.dom.pulldom.END_DOCUMENT

The start and the end of the document. node is the Document.

xml.dom.pulldom.START_ELEMENT

xml.dom.pulldom.END_ELEMENT

The start tag and the end tag of an element. node is the Element.

xml.dom.pulldom.CHARACTERS

Character data. node is the Text node.

xml.dom.pulldom.IGNORABLE_WHITESPACE

White space in element content, as declared in the DTD. node is the Text node.

xml.dom.pulldom.COMMENT

A comment. node is the Comment node.

xml.dom.pulldom.PROCESSING_INSTRUCTION

A processing instruction. node is the ProcessingInstruction node.

Puesto que el documento se trata como una secuencia «flat» (plana) de eventos, el documento «tree» (árbol) se atraviesa implícitamente y los elementos deseados se encuentran independientemente de su profundidad en el árbol. En otras palabras, no es necesario tener en cuenta cuestiones jerárquicas como la búsqueda recursiva de los nodos de documento, aunque si el contexto de los elementos fuera importante, es necesario mantener algún estado relacionado con el contexto (es decir, recordar dónde se encuentra en el documento en un momento dado) o hacer uso del método DOMEventStream.expandNode() y cambiar al procesamiento relacionado con DOM.

class xml.dom.pulldom.PullDOM(documentFactory=None)

Subclass of xml.sax.handler.ContentHandler which turns SAX events into the events of the pull parser. The nodes are created, but they are not added to the tree, unless expandNode() is called. documentFactory, if given, is a DOM implementation used to create the document; by default the implementation of xml.dom.minidom is used.

class xml.dom.pulldom.SAX2DOM(documentFactory=None)

Subclass of PullDOM which also adds every created node to the tree, so that the complete document is built.

xml.dom.pulldom.parse(stream_or_string, parser=None, bufsize=None)

Retorna un DOMEventStream de la entrada dada. stream_or_string (secuencia o cadena) puede ser un nombre de archivo o un objeto similar a un archivo, parser, si se indica, debe ser un objeto XMLReader. Esta función cambiará el controlador de documentos del analizador y activará el soporte de espacios de nombres; otra configuración del analizador (como establecer un solucionador de entidades) debe haberse realizado de antemano.

Si tiene XML en una cadena, puede usar en su lugar la función parseString():

xml.dom.pulldom.parseString(string, parser=None)

Return a DOMEventStream that represents the string. string must be a str instance; to parse bytes, pass a binary file object to parse().

xml.dom.pulldom.default_bufsize

Valor predeterminado para el parámetro bufsize para parse().

El valor de las variables puede ser cambiado antes de llamar a parse() y el nuevo valor tendrá efecto.

Objetos DOMEventStream

class xml.dom.pulldom.DOMEventStream(stream, parser, bufsize)

Produce the events for the data read from the file object stream by the XMLReader parser. The data is read by bufsize bytes, or characters for a text stream, at a time.

Distinto en la versión 3.11: Support for __getitem__() method has been removed.

getEvent()

Return the next (event, node) tuple, or None at the end of the document. See above for the events and the corresponding nodes. The current node does not contain information about its children, unless expandNode() is called.

expandNode(node)

Expande todos los hijos de node en node (nodo en nodo). Ejemplo:

from xml.dom import pulldom

xml = '<html><title>Foo</title> <p>Some text <div>and more</div></p> </html>'
doc = pulldom.parseString(xml)
for event, node in doc:
    if event == pulldom.START_ELEMENT and node.tagName == 'p':
        # Following statement only prints '<p/>'
        print(node.toxml())
        doc.expandNode(node)
        # Following statement prints node with all its children '<p>Some text <div>and more</div></p>'
        print(node.toxml())

reset()

Discard the events which are not read yet and prepare the object for parsing a new document.

clear()

Release the parser and the document. The stream is not closed, and the object can no longer be used.