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annotate doc/xpath.txt @ 442:ff7c72b52fb2

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Back out [510] and instead implement configurable error handling modes. The default is the old 0.3.x behaviour, but more strict error handling is available as an option.
author cmlenz
date Thu, 12 Apr 2007 22:40:49 +0000
parents ebc7c1a3bc4d
children ca7d707d51b0 1837f39efd6f
rev   line source
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1 .. -*- mode: rst; encoding: utf-8 -*-
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2
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3 =====================
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4 Using XPath in Genshi
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5 =====================
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6
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7 Genshi provides basic XPath_ support for matching and querying event streams.
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8
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9 .. _xpath: http://www.w3.org/TR/xpath
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10
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11
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12 .. contents:: Contents
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13 :depth: 2
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14 .. sectnum::
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15
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16
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17 -----------
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18 Limitations
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19 -----------
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20
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21 Due to the streaming nature of the processing model, Genshi uses only a subset
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22 of the `XPath 1.0`_ language.
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23
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24 .. _`XPath 1.0`: http://www.w3.org/TR/xpath
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25
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26 In particular, only the following axes are supported:
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27
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28 * ``attribute``
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29 * ``child``
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30 * ``descendant``
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31 * ``descendant-or-self``
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32 * ``self``
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33
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34 This means you can't use the ``parent``, ancestor, or sibling axes in Genshi
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35 (the ``namespace`` axis isn't supported either, but what you'd ever need that
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36 for I don't know). Basically, any path expression that would require buffering
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37 of the stream is not supported.
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38
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39 Predicates are of course supported, but path expressions *inside* predicates
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40 are restricted to attribute lookups (again due to the lack of buffering).
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41
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42 Most of the XPath functions and operators are supported, however they
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43 (currently) only work inside predicates. The following functions are **not**
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44 supported:
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45
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46 * ``count()``
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47 * ``id()``
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48 * ``lang()``
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49 * ``last()``
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50 * ``position()``
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51 * ``string()``
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52 * ``sum()``
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53
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54 The mathematical operators (``+``, ``-``, ``*``, ``div``, and ``mod``) are not
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55 yet supported, whereas the various comparison and logical operators should work
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56 as expected.
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57
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58 You can also use XPath variable references (``$var``) inside predicates.
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59
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60
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61 ----------------
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62 Querying Streams
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63 ----------------
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64
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65 ::
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66
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67 from genshi.input import XML
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68
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69 doc = XML('''<doc>
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70 <items count="2">
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71 <item status="new">
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72 <summary>Foo</summary>
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73 </item>
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74 <item status="closed">
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75 <summary>Bar</summary>
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76 </item>
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77 </items>
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78 </doc>''')
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79 print doc.select('items/item[@status="closed"]/summary/text()')
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80
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81 This would result in the following output::
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82
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83 Bar
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84
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85
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86 ---------------------
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87 Matching in Templates
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88 ---------------------
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89
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90 See the directive ``py:match`` in the `XML Template Language Specification`_.
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91
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92 .. _`XML Template Language Specification`: xml-templates.html
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