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

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

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.

Note

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

Changed in version 3.7.1: The SAX parser no longer processes general external entities by default to increase security by default. To enable processing of external entities, pass a 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)

Example:

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.

Since the document is treated as a “flat” stream of events, the document “tree” is implicitly traversed and the desired elements are found regardless of their depth in the tree. In other words, one does not need to consider hierarchical issues such as recursive searching of the document nodes, although if the context of elements were important, one would either need to maintain some context-related state (i.e. remembering where one is in the document at any given point) or to make use of the DOMEventStream.expandNode() method and switch to DOM-related processing.

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)

Return a DOMEventStream from the given input. stream_or_string may be either a file name, or a file-like object. parser, if given, must be an XMLReader object. This function will change the document handler of the parser and activate namespace support; other parser configuration (like setting an entity resolver) must have been done in advance.

If you have XML in a string, you can use the parseString() function instead:

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

Default value for the bufsize parameter to parse().

The value of this variable can be changed before calling parse() and the new value will take effect.

DOMEventStream Objects

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.

Changed in version 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)

Expands all children of node into node. Example:

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.