| 1 | | {{{ |
| 2 | | #!rst |
| 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 | | }}} |
| | 1 | [[Include(trunk/doc/xpath.txt)]] |
