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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 The ``Stream`` class provides a ``select(path)`` function that can be used to
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66 retrieve subsets of the stream:
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67
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68 .. code-block:: pycon
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69
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70 >>> from genshi.input import XML
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71
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72 >>> doc = XML('''<doc>
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73 ... <items count="2">
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74 ... <item status="new">
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75 ... <summary>Foo</summary>
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76 ... </item>
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77 ... <item status="closed">
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78 ... <summary>Bar</summary>
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79 ... </item>
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80 ... </items>
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81 ... </doc>''')
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82
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83 >>> print doc.select('items/item[@status="closed"]/summary/text()')
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84 Bar
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85
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86
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87 ---------------------
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88 Matching in Templates
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89 ---------------------
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90
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91 See the directive ``py:match`` in the `XML Template Language Specification`_.
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92
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93 .. _`XML Template Language Specification`: xml-templates.html
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