Mercurial > genshi > genshi-test
comparison doc/xpath.txt @ 226:09f869a98149
Add reStructuredText documentation files.
| author | cmlenz |
|---|---|
| date | Fri, 08 Sep 2006 08:44:31 +0000 |
| parents | |
| children | 24757b771651 |
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| 225:0edf663b97d6 | 226:09f869a98149 |
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| 1 .. -*- mode: rst; encoding: utf-8 -*- | |
| 2 | |
| 3 ===================== | |
| 4 Using XPath in Markup | |
| 5 ===================== | |
| 6 | |
| 7 Markup provides basic XPath_ support for matching and querying event streams. | |
| 8 | |
| 9 .. _xpath: http://www.w3.org/TR/xpath | |
| 10 | |
| 11 | |
| 12 .. contents:: Contents | |
| 13 :depth: 2 | |
| 14 .. sectnum:: | |
| 15 | |
| 16 | |
| 17 ----------- | |
| 18 Limitations | |
| 19 ----------- | |
| 20 | |
| 21 Due to the streaming nature of the processing model, Markup uses only a subset | |
| 22 of the `XPath 1.0`_ language. | |
| 23 | |
| 24 .. _`XPath 1.0`: http://www.w3.org/TR/xpath | |
| 25 | |
| 26 In particular, only the following axes are supported: | |
| 27 | |
| 28 * ``attribute`` | |
| 29 * ``child`` | |
| 30 * ``descendant`` | |
| 31 * ``descendant-or-self`` | |
| 32 * ``self`` | |
| 33 | |
| 34 This means you can't use the ``parent``, ancestor, or sibling axes in Markup | |
| 35 (the ``namespace`` axis isn't supported either, but what you'd ever need that | |
| 36 for I don't know). Basically, any path expression that would require buffering | |
| 37 of the stream is not supported. | |
| 38 | |
| 39 Predicates are of course supported, but Path expressions *inside* predicates | |
| 40 are restricted to attribute lookups (again due to the lack of buffering). | |
| 41 | |
| 42 Most of the XPath functions and operators are supported, however they | |
| 43 (currently) only work inside predicates. The following functions are **not** | |
| 44 supported: | |
| 45 | |
| 46 * ``count()`` | |
| 47 * ``id()`` | |
| 48 * ``lang()`` | |
| 49 * ``last()`` | |
| 50 * ``position()`` | |
| 51 * ``string()`` | |
| 52 * ``sum()`` | |
| 53 | |
| 54 The mathematical operators (``+``, ``-``, ``*``, ``div``, and ``mod``) are not | |
| 55 yet supported, whereas the various comparison and logical operators should work | |
| 56 as expected. | |
| 57 | |
| 58 You can also use XPath variable references (``$var``) inside predicates. | |
| 59 | |
| 60 | |
| 61 ---------------- | |
| 62 Querying Streams | |
| 63 ---------------- | |
| 64 | |
| 65 :: | |
| 66 | |
| 67 from markup.input import XML | |
| 68 | |
| 69 doc = XML('''<doc> | |
| 70 <items count="2"> | |
| 71 <item status="new"> | |
| 72 <summary>Foo</summary> | |
| 73 </item> | |
| 74 <item status="closed"> | |
| 75 <summary>Bar</summary> | |
| 76 </item> | |
| 77 </items> | |
| 78 </doc>''') | |
| 79 print doc.select('items/item[@status="closed"]/summary/text()') | |
| 80 | |
| 81 This would result in the following output:: | |
| 82 | |
| 83 Bar | |
| 84 | |
| 85 | |
| 86 --------------------- | |
| 87 Matching in Templates | |
| 88 --------------------- | |
| 89 | |
| 90 See the directive ``py:match`` in the `XML Template Language Specification`_. | |
| 91 | |
| 92 .. _`XML Template Language Specification`: xml-templates.html |