[lxml-dev] About objectify

[jholg at gmx.de]

Hi David,



> Does anyone have a simple example with a short XML file containing some
> elements, its schema, and the python code parsing the file using
> objectify with the xsi namespace to do type association ?
> 
> 




I'm not quite sure I understand what you try to achieve,

but lxml.objectify does not necessarily need a schema:

  $ cat simpleInstance.xml
<root>
    <s>A string, hopefully.</s>
</root>

  You can simply parse this using objecify:

 >>> from lxml import etree, objectify
>>> root = objectify.parse("simpleInstance.xml").getroot()
>>> print objectify.dump(root)
root = None [ObjectifiedElement]
    s = 'A string, hopefully.' [StringElement]
>>> print root.s
A string, hopefully.
>>>

 What you can do is validate this XML tree against a schema:

 $ cat simpleSchema.xsd
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
 
  <xsd:element name="root" type="RootType"/>
 
  <xsd:complexType name="RootType">
    <xsd:sequence>
      <xsd:element name="s" type="xsd:string"/>
    </xsd:sequence>
  </xsd:complexType>
</xsd:schema> 

 >>> from lxml import etree, objectify
>>> root = objectify.parse("simpleInstance.xml").getroot()
>>> schema = etree.XMLSchema(objectify.parse("simpleSchema.xsd"))
>>> schema.validate(root)
True
>>> 
 No xsi:type information anywhere, so far.

 What you currently can not do is use the schema to *add* xsi:type 
attributes

to the XML instance. Or, to put it another way, schema-validation does not

add any type-information. 

 No problem, though, if the XML contains xsi:type information:

 >>> from lxml import etree, objectify
>>> root = objectify.parse("simpleInstance2.xml").getroot()
>>> print objectify.dump(root)
root = None [ObjectifiedElement]
    s = 'A string, hopefully.' [StringElement]
      * xsi:type = 'xsd:normalizedString'
>>> print root.s
A string, hopefully.
>>> schema = etree.XMLSchema(objectify.parse("simpleSchema.xsd"))
>>> schema.validate(root)
True
>>>

 If xsi:type information is available, it will be used to determine the 
lxml.objectify

type representation of an element:

Consider

 >>> root = objectify.fromstring("<root><s>3</s></root>")
>>> print objectify.dump(root)
root = None [ObjectifiedElement]
    s = 3 [IntElement]
>>>

 vs.

 >>> root = objectify.fromstring("""
... <root xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
...       xmlns:xsd="http://www.w3.org/2001/XMLSchema">
... <s xsi:type="xsd:string">3</s>
... </root>""")
>>> print objectify.dump(root)
root = None [ObjectifiedElement]
    s = '3' [StringElement]
      * xsi:type = 'xsd:string'
>>>
 HTH,

Holger 

 
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