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131 lines
4.6 KiB
ReStructuredText
131 lines
4.6 KiB
ReStructuredText
:mod:`xml.dom.pulldom` --- Support for building partial DOM trees
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=================================================================
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.. module:: xml.dom.pulldom
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:synopsis: Support for building partial DOM trees from SAX events.
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.. moduleauthor:: Paul Prescod <paul@prescod.net>
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**Source code:** :source:`Lib/xml/dom/pulldom.py`
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--------------
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The :mod:`xml.dom.pulldom` module provides a "pull parser" which can also be
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asked to produce DOM-accessible fragments of the document where necessary. The
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basic concept involves pulling "events" from a stream of incoming XML and
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processing them. In contrast to SAX which also employs an event-driven
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processing model together with callbacks, the user of a pull parser is
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responsible for explicitly pulling events from the stream, looping over those
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events until either processing is finished or an error condition occurs.
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.. warning::
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The :mod:`xml.dom.pulldom` module is not secure against
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maliciously constructed data. If you need to parse untrusted or
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unauthenticated data see :ref:`xml-vulnerabilities`.
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Example::
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from xml.dom import pulldom
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doc = pulldom.parse('sales_items.xml')
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for event, node in doc:
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if event == pulldom.START_ELEMENT and node.tagName == 'item':
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if int(node.getAttribute('price')) > 50:
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doc.expandNode(node)
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print(node.toxml())
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``event`` is a constant and can be one of:
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* :data:`START_ELEMENT`
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* :data:`END_ELEMENT`
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* :data:`COMMENT`
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* :data:`START_DOCUMENT`
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* :data:`END_DOCUMENT`
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* :data:`CHARACTERS`
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* :data:`PROCESSING_INSTRUCTION`
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* :data:`IGNORABLE_WHITESPACE`
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``node`` is an object of type :class:`xml.dom.minidom.Document`,
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:class:`xml.dom.minidom.Element` or :class:`xml.dom.minidom.Text`.
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Since the document is treated as a "flat" stream of events, the document "tree"
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is implicitly traversed and the desired elements are found regardless of their
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depth in the tree. In other words, one does not need to consider hierarchical
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issues such as recursive searching of the document nodes, although if the
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context of elements were important, one would either need to maintain some
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context-related state (i.e. remembering where one is in the document at any
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given point) or to make use of the :func:`DOMEventStream.expandNode` method
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and switch to DOM-related processing.
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.. class:: PullDom(documentFactory=None)
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Subclass of :class:`xml.sax.handler.ContentHandler`.
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.. class:: SAX2DOM(documentFactory=None)
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Subclass of :class:`xml.sax.handler.ContentHandler`.
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.. function:: parse(stream_or_string, parser=None, bufsize=None)
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Return a :class:`DOMEventStream` from the given input. *stream_or_string* may be
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either a file name, or a file-like object. *parser*, if given, must be an
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:class:`~xml.sax.xmlreader.XMLReader` object. This function will change the
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document handler of the
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parser and activate namespace support; other parser configuration (like
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setting an entity resolver) must have been done in advance.
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If you have XML in a string, you can use the :func:`parseString` function instead:
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.. function:: parseString(string, parser=None)
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Return a :class:`DOMEventStream` that represents the (Unicode) *string*.
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.. data:: default_bufsize
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Default value for the *bufsize* parameter to :func:`parse`.
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The value of this variable can be changed before calling :func:`parse` and
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the new value will take effect.
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.. _domeventstream-objects:
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DOMEventStream Objects
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----------------------
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.. class:: DOMEventStream(stream, parser, bufsize)
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.. method:: getEvent()
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Return a tuple containing *event* and the current *node* as
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:class:`xml.dom.minidom.Document` if event equals :data:`START_DOCUMENT`,
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:class:`xml.dom.minidom.Element` if event equals :data:`START_ELEMENT` or
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:data:`END_ELEMENT` or :class:`xml.dom.minidom.Text` if event equals
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:data:`CHARACTERS`.
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The current node does not contain information about its children, unless
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:func:`expandNode` is called.
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.. method:: expandNode(node)
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Expands all children of *node* into *node*. Example::
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from xml.dom import pulldom
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xml = '<html><title>Foo</title> <p>Some text <div>and more</div></p> </html>'
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doc = pulldom.parseString(xml)
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for event, node in doc:
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if event == pulldom.START_ELEMENT and node.tagName == 'p':
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# Following statement only prints '<p/>'
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print(node.toxml())
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doc.expandNode(node)
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# Following statement prints node with all its children '<p>Some text <div>and more</div></p>'
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print(node.toxml())
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.. method:: DOMEventStream.reset()
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