| 1 | | {{{ |
| 2 | | #!rst |
| 3 | | ============== |
| 4 | | Markup Streams |
| 5 | | ============== |
| 6 | | |
| 7 | | A stream is the common representation of markup as a *stream of events*. |
| 8 | | |
| 9 | | |
| 10 | | .. contents:: Contents |
| 11 | | :depth: 2 |
| 12 | | .. sectnum:: |
| 13 | | |
| 14 | | |
| 15 | | Basics |
| 16 | | ====== |
| 17 | | |
| 18 | | A stream can be attained in a number of ways. It can be: |
| 19 | | |
| 20 | | * the result of parsing XML or HTML text, or |
| 21 | | * programmatically generated, or |
| 22 | | * the result of selecting a subset of another stream filtered by an XPath |
| 23 | | expression. |
| 24 | | |
| 25 | | For example, the functions ``XML()`` and ``HTML()`` can be used to convert |
| 26 | | literal XML or HTML text to a markup stream:: |
| 27 | | |
| 28 | | >>> from markup import XML |
| 29 | | >>> stream = XML('<p class="intro">Some text and ' |
| 30 | | ... '<a href="http://example.org/">a link</a>.' |
| 31 | | ... '<br/></p>') |
| 32 | | >>> stream |
| 33 | | <markup.core.Stream object at 0x6bef0> |
| 34 | | |
| 35 | | The stream is the result of parsing the text into events. Each event is a tuple |
| 36 | | of the form ``(kind, data, pos)``, where: |
| 37 | | |
| 38 | | * ``kind`` defines what kind of event it is (such as the start of an element, |
| 39 | | text, a comment, etc). |
| 40 | | * ``data`` is the actual data associated with the event. How this looks depends |
| 41 | | on the event kind. |
| 42 | | * ``pos`` is a ``(filename, lineno, column)`` tuple that describes where the |
| 43 | | event “comes from”. |
| 44 | | |
| 45 | | :: |
| 46 | | |
| 47 | | >>> for kind, data, pos in stream: |
| 48 | | ... print kind, `data`, pos |
| 49 | | ... |
| 50 | | START (u'p', [(u'class', u'intro')]) ('<string>', 1, 0) |
| 51 | | TEXT u'Some text and ' ('<string>', 1, 31) |
| 52 | | START (u'a', [(u'href', u'http://example.org/')]) ('<string>', 1, 31) |
| 53 | | TEXT u'a link' ('<string>', 1, 67) |
| 54 | | END u'a' ('<string>', 1, 67) |
| 55 | | TEXT u'.' ('<string>', 1, 72) |
| 56 | | START (u'br', []) ('<string>', 1, 72) |
| 57 | | END u'br' ('<string>', 1, 77) |
| 58 | | END u'p' ('<string>', 1, 77) |
| 59 | | |
| 60 | | |
| 61 | | Filtering |
| 62 | | ========= |
| 63 | | |
| 64 | | One important feature of markup streams is that you can apply *filters* to the |
| 65 | | stream, either filters that come with Markup, or your own custom filters. |
| 66 | | |
| 67 | | A filter is simply a callable that accepts the stream as parameter, and returns |
| 68 | | the filtered stream:: |
| 69 | | |
| 70 | | def noop(stream): |
| 71 | | """A filter that doesn't actually do anything with the stream.""" |
| 72 | | for kind, data, pos in stream: |
| 73 | | yield kind, data, pos |
| 74 | | |
| 75 | | Filters can be applied in a number of ways. The simplest is to just call the |
| 76 | | filter directly:: |
| 77 | | |
| 78 | | stream = noop(stream) |
| 79 | | |
| 80 | | The ``Stream`` class also provides a ``filter()`` method, which takes an |
| 81 | | arbitrary number of filter callables and applies them all:: |
| 82 | | |
| 83 | | stream = stream.filter(noop) |
| 84 | | |
| 85 | | Finally, filters can also be applied using the *bitwise or* operator (``|``), |
| 86 | | which allows a syntax similar to pipes on Unix shells:: |
| 87 | | |
| 88 | | stream = stream | noop |
| 89 | | |
| 90 | | One example of a filter included with Markup is the ``HTMLSanitizer`` in |
| 91 | | ``markup.filters``. It processes a stream of HTML markup, and strips out any |
| 92 | | potentially dangerous constructs, such as Javascript event handlers. |
| 93 | | ``HTMLSanitizer`` is not a function, but rather a class that implements |
| 94 | | ``__call__``, which means instances of the class are callable. |
| 95 | | |
| 96 | | Both the ``filter()`` method and the pipe operator allow easy chaining of |
| 97 | | filters:: |
| 98 | | |
| 99 | | from markup.filters import HTMLSanitizer |
| 100 | | stream = stream.filter(noop, HTMLSanitizer()) |
| 101 | | |
| 102 | | That is equivalent to:: |
| 103 | | |
| 104 | | stream = stream | noop | HTMLSanitizer() |
| 105 | | |
| 106 | | |
| 107 | | Serialization |
| 108 | | ============= |
| 109 | | |
| 110 | | The ``Stream`` class provides two methods for serializing this list of events: |
| 111 | | ``serialize()`` and ``render()``. The former is a generator that yields chunks |
| 112 | | of ``Markup`` objects (which are basically unicode strings). The latter returns |
| 113 | | a single string, by default UTF-8 encoded. |
| 114 | | |
| 115 | | Here's the output from ``serialize()``:: |
| 116 | | |
| 117 | | >>> for output in stream.serialize(): |
| 118 | | ... print `output` |
| 119 | | ... |
| 120 | | <Markup u'<p class="intro">'> |
| 121 | | <Markup u'Some text and '> |
| 122 | | <Markup u'<a href="http://example.org/">'> |
| 123 | | <Markup u'a link'> |
| 124 | | <Markup u'</a>'> |
| 125 | | <Markup u'.'> |
| 126 | | <Markup u'<br/>'> |
| 127 | | <Markup u'</p>'> |
| 128 | | |
| 129 | | And here's the output from ``render()``:: |
| 130 | | |
| 131 | | >>> print stream.render() |
| 132 | | <p class="intro">Some text and <a href="http://example.org/">a link</a>.<br/></p> |
| 133 | | |
| 134 | | Both methods can be passed a ``method`` parameter that determines how exactly |
| 135 | | the events are serialzed to text. This parameter can be either “xml” (the |
| 136 | | default), “xhtml”, “html”, “text”, or a custom serializer class:: |
| 137 | | |
| 138 | | >>> print stream.render('html') |
| 139 | | <p class="intro">Some text and <a href="http://example.org/">a link</a>.<br></p> |
| 140 | | |
| 141 | | Note how the `<br>` element isn't closed, which is the right thing to do for |
| 142 | | HTML. |
| 143 | | |
| 144 | | In addition, the ``render()`` method takes an ``encoding`` parameter, which |
| 145 | | defaults to “UTF-8”. If set to ``None``, the result will be a unicode string. |
| 146 | | |
| 147 | | The different serializer classes in ``markup.output`` can also be used |
| 148 | | directly:: |
| 149 | | |
| 150 | | >>> from markup.filters import HTMLSanitizer |
| 151 | | >>> from markup.output import TextSerializer |
| 152 | | >>> print TextSerializer()(HTMLSanitizer()(stream)) |
| 153 | | Some text and a link. |
| 154 | | |
| 155 | | The pipe operator allows a nicer syntax:: |
| 156 | | |
| 157 | | >>> print stream | HTMLSanitizer() | TextSerializer() |
| 158 | | Some text and a link. |
| 159 | | |
| 160 | | Using XPath |
| 161 | | =========== |
| 162 | | |
| 163 | | XPath can be used to extract a specific subset of the stream via the |
| 164 | | ``select()`` method:: |
| 165 | | |
| 166 | | >>> substream = stream.select('a') |
| 167 | | >>> substream |
| 168 | | <markup.core.Stream object at 0x7118b0> |
| 169 | | >>> print substream |
| 170 | | <a href="http://example.org/">a link</a> |
| 171 | | |
| 172 | | Often, streams cannot be reused: in the above example, the sub-stream is based |
| 173 | | on a generator. Once it has been serialized, it will have been fully consumed, |
| 174 | | and cannot be rendered again. To work around this, you can wrap such a stream |
| 175 | | in a ``list``:: |
| 176 | | |
| 177 | | >>> from markup import Stream |
| 178 | | >>> substream = Stream(list(stream.select('a'))) |
| 179 | | >>> substream |
| 180 | | <markup.core.Stream object at 0x7118b0> |
| 181 | | >>> print substream |
| 182 | | <a href="http://example.org/">a link</a> |
| 183 | | >>> print substream.select('@href') |
| 184 | | http://example.org/ |
| 185 | | >>> print substream.select('text()') |
| 186 | | a link |
| 187 | | }}} |
| 188 | | |
| | 1 | [[Include(trunk/doc/streams.txt)]] |
