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Simple/Basic parsing of XML using SAX

XMLParser parses XML data sent to its "inbox" inbox using SAX, and sends out "document", "element" and "character" events out of its "outbox" outbox.

Example Usage

The following code:

Pipeline( RateControlledFileReader("Myfile.xml"),

If given the following file as input:

<EDL xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="MobileReframe.xsd">>
    <FileID>File identifier</FileID>

        <Start frame="0"  />
        <End   frame="24" />
        <Crop  x1="0" y1="0" x2="400" y2="100" />
        <Start frame="25" />
        <End   frame="49" />
        <Crop  x1="80" y1="40" x2="480" y2="140" />

Will output the following (albeit without the newlines, added here for clarity):

('element', u'EDL', <xml.sax.xmlreader.AttributesImpl instance at 0x2aaaaca86e60>)
('chars', u'>')
('chars', u'\n')
('chars', u'    ')
('element', u'FileID', <xml.sax.xmlreader.AttributesImpl instance at 0x2aaaac028758>)
('chars', u'File identifier')
('/element', u'FileID')
('chars', u'\n')
('chars', u'    ')
('chars', u'\n')
('chars', u'    ')
('element', u'Edit', <xml.sax.xmlreader.AttributesImpl instance at 0x2aaaac028908>)
('chars', u'\n')
('chars', u'        ')
('element', u'Start', <xml.sax.xmlreader.AttributesImpl instance at 0x2aaaac028908>)
('/element', u'Start')
('chars', u'\n')
('chars', u'        ')
('element', u'End', <xml.sax.xmlreader.AttributesImpl instance at 0x2aaaaca86e60>)
('/element', u'End')
('chars', u'\n')
('chars', u'        ')
('element', u'Crop', <xml.sax.xmlreader.AttributesImpl instance at 0x2aaaac028908>)
('/element', u'Crop')
('chars', u'\n')
('chars', u'    ')
('/element', u'Edit')
('chars', u'\n')
('chars', u'    ')
('/element', u'EDL')

What does it output?

What is output is effectively a simple, but useful, parsing of the XML. It is a set of messages representing a subset of the python SAX ContentHandler. All are in the form of a simple tuple where the first term is always the type of "thing" identified - 'document' start or finish, 'element' start or finish, or raw text characters:

``("document", )``

  • Start of the XML document

``("/document", )``

  • End of the XML document (not sent if shutdown with a shutdownMicroprocess() message)

``("element", name, attributes)``

  • Start tag for an element. name is the name of the element. attributes is a SAX attributes object - which behaves just like a dictionary - mapping attribute names to strings of their values. For example:

    ("element", "img", {"src":"/images/mypic.jpg"})

``("/element", name)``

  • End tag for an element. name is the name of the element.

``("chars", textfragment)``

  • Fragment of text from within an element. Note that the text contained in a single element be comprised of multiple fragments. They will include whitespace and newline characters.


Send chunks of text making up an XML document to this component's "inbox" inbox. The XML Parser used will output identified items from its "outbox" outbox.

This component supports sending its output to a size limited inbox. If the size limited inbox is full, this component will pause until it is able to send out the data.

If a producerFinished message is received on the "control" inbox, this component will complete parsing any data pending in its inbox, and finish sending any resulting data to its outbox. It will then send the producerFinished message on out of its "signal" outbox and terminate.

If a shutdownMicroprocess message is received on the "control" inbox, this component will immediately send it on out of its "signal" outbox and immediately terminate. It will not complete processing, or sending on any pending data.


class SimpleXMLParser(Axon.Component.component, xml.sax.handler.ContentHandler)

SimpleXMLParser() -> new SimpleXMLParser component.

Send XML data to the "inbox" inbox, and events describing documents, elements and blocks of characters (as parsed by SAX) will be sent out of the "outbox" outbox.


  • control : Shutdown signalling
  • inbox : Incoming XML


  • outbox : XML events
  • signal : Shutdown signalling

Methods defined here


You should be using the inbox/outbox interface, not these methods (except construction). This documentation is designed as a roadmap as to their functionalilty for maintainers and new component developers.


characters(self, chars)


Collects any new shutdown messages arriving at the "control" inbox, and returns "NOW" if immediate shutdown is required, or "WHENEVER" if the component can shutdown when it has finished processing pending data.


endElement(self, name)


safesend(self, data, boxname)


Sends data out of the named outbox. If the destination is full (noSpaceInBox exception) then it waits until there is space and retries until it succeeds.

If a shutdownMicroprocess message is received, returns early.


startElement(self, name, attrs)


Got a problem with the documentation? Something unclear that could be clearer? Want to help improve it? Constructive criticism is very welcome - especially if you can suggest a better rewording!

Please leave you feedback here in reply to the documentation thread in the Kamaelia blog.

-- Automatic documentation generator, 05 Jun 2009 at 03:01:38 UTC/GMT