Edgewall Software
Version 2 (modified by cmlenz, 8 years ago)

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Markup Streams

A stream? is the common representation of markup as a stream of events.

A stream can be attained in a number of ways. It can be:

  • the result of parsing XML or HTML text, or
  • programmatically generated, or
  • the result of selecting a subset of another stream filtered by an XPath expression.

For example, the functions XML() and HTML() can be used to convert literal XML or HTML text to a markup stream:

>>> from markup import XML
>>> stream = XML('<p class="intro">Some text and '
...              '<a href="http://example.org/">a link</a>.'
...              '<br/></p>')
>>> stream
<markup.core.Stream object at 0x6bef0>

The stream is the result of parsing the text into events. Each event is a tuple of the form (kind, data, pos), where:

  • kind defines what kind of event it is (such as the start of an element, text, a comment, etc).
  • data is the actual data associated with the event. How this looks depends on the event kind.
  • pos is a (filename, lineno, column) tuple that describes where the event “comes from”.
>>> for kind, data, pos in stream:
...     print kind, `data`, pos
... 
START (u'p', [(u'class', u'intro')]) ('<string>', 1, 0)
TEXT u'Some text and ' ('<string>', 1, 31)
START (u'a', [(u'href', u'http://example.org/')]) ('<string>', 1, 31)
TEXT u'a link' ('<string>', 1, 67)
END u'a' ('<string>', 1, 67)
TEXT u'.' ('<string>', 1, 72)
START (u'br', []) ('<string>', 1, 72)
END u'br' ('<string>', 1, 77)
END u'p' ('<string>', 1, 77)

Serialization

The Stream class provides two methods for serializing this list of events: serialize()? and render()?. The former is a generator that yields chunks of Markup objects (which are basically unicode strings). The latter returns a single string, by default UTF-8 encoded.

Here's the output from serialize():

>>> for output in stream.serialize():
...     print `output`
... 
<Markup u'<p class="intro">'>
<Markup u'Some text and '>
<Markup u'<a href="http://example.org/">'>
<Markup u'a link'>
<Markup u'</a>'>
<Markup u'.'>
<Markup u'<br/>'>
<Markup u'</p>'>

And here's the output from render():

>>> print stream.render()
<p class="intro">Some text and <a href="http://example.org/">a link</a>.<br/></p>

Both methods can be passed a method parameter that determines how exactly the events are serialzed to text. This parameter can be either “xml” (the default) or “html”, or a subclass of the markup.output.Serializer class:

>>> print stream.render('html')
<p class="intro">Some text and <a href="http://example.org/">a link</a>.<br></p>

(Note how the <br> element isn't closed, which is the right thing to do for HTML.)

In addition, the render() method takes an encoding parameter, which defaults to “UTF-8”. If set to None, the result will be a unicode string.

Using XPath

XPath can be used to extract a specific subset of the stream via the select() method:

>>> substream = stream.select('a')
>>> substream
<markup.core.Stream object at 0x7118b0>
>>> print substream
<a href="http://example.org/">a link</a>

See also: MarkupGuide?