Hi,

> What I was hoping for is the following:
> 1.       I was hoping objectify would be enforcing the object tree
> specified in the schema for both elements and attributes (I realized
> after rereading the documentation paragraph above that it only
> promises to do so for attributes)

According to http://xmlsoft.org/html/libxml-xmlschemas.html:

Enum xmlSchemaValidOption {
    XML_SCHEMA_VAL_VC_I_CREATE = 1 : Default/fixed: create an attribute
node * or an element's text node on the instance. *
}

This is the option that's set by using attribute_defaults=True in lxml, so
in theory
it should work for both missing attributes and empty elements.
(Don't know if you need it in the XMLSchema constructor or the makeparser
function or both).

> 2.       Objectify would be able to assign the default value
> specified in the schema for simple elements (which it does correctly
> for attributes)

Note that minOccurs=0 elements shall not be defaulted if missing according
to XML Schema rec,
see e.g.
https://lists.w3.org/Archives/Public/xmlschema-dev/2001Apr/0059.html
for some background.
I.e. missing elements are never created through default="...".

However in practice:

>>> schemadoc = etree.fromstring("""
... <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
...   <xs:element name="root">
...     <xs:complexType>
...       <xs:sequence>
...         <xs:element name="elem" minOccurs="0" maxOccurs="unbounded">
...           <xs:complexType>
...             <xs:sequence>
...               <xs:element name="a" type="xs:int" minOccurs="0"
maxOccurs="1" default="0"/>
...             </xs:sequence>
...           </xs:complexType>
...         </xs:element>
...       </xs:sequence>
...     </xs:complexType>
...   </xs:element>
... </xs:schema>
... """)
>>>
>>> schema = etree.XMLSchema(schemadoc, attribute_defaults=True)
>>> parser = objectify.makeparser(schema=schema)
>>>
>>> xml = """
... <root>
...   <elem></elem>
...   <elem><a/></elem>
...   <elem><a></a></elem>
...   <elem><a>42</a></elem>
... </root>
... """
>>>
>>> root = objectify.fromstring(xml, parser=parser)
>>>
>>> print(objectify.dump(root))
root = None [ObjectifiedElement]
    elem = u'' [StringElement]
    elem = None [ObjectifiedElement]
        a = u'' [StringElement]
    elem = None [ObjectifiedElement]
        a = u'' [StringElement]
    elem = None [ObjectifiedElement]
        a = 42 [IntElement]
>>>

I.e. a's text content is never defaulted to 0 contrary to what we expect.

Now, if I slightly modify the validating schema and add a default attribute
to
the root element but leave the instance document untouched:

>>> schemadoc = etree.fromstring("""
... <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
...   <xs:element name="root">
...     <xs:complexType>
...       <xs:sequence>
...         <xs:element name="elem" minOccurs="0" maxOccurs="unbounded">
...           <xs:complexType>
...             <xs:sequence>
...               <xs:element name="a" type="xs:int" minOccurs="0"
maxOccurs="1" default="0"/>
...             </xs:sequence>
...           </xs:complexType>
...         </xs:element>
...       </xs:sequence>
...       <xs:attribute name="elem_attr" default="default value"/>
...     </xs:complexType>
...   </xs:element>
... </xs:schema>
... """)
>>>
>>> schema = etree.XMLSchema(schemadoc, attribute_defaults=True)
>>> parser = objectify.makeparser(schema=schema)
>>>
>>> xml = """
... <root>
...   <elem></elem>
...   <elem><a/></elem>
...   <elem><a></a></elem>
...   <elem><a>42</a></elem>
... </root>
... """
>>>
>>>
>>> root = objectify.fromstring(xml, parser=parser)
>>>
>>> print(objectify.dump(root))
root = None [ObjectifiedElement]
  * elem_attr = 'default value'
    elem = u'' [StringElement]
    elem = None [ObjectifiedElement]
        a = 0 [IntElement]
    elem = None [ObjectifiedElement]
        a = 0 [IntElement]
    elem = None [ObjectifiedElement]
        a = 42 [IntElement]
>>>

Hm. Now we see both the root attribute get defaulted *and* the element text
content.
Strange - I suspect a bug in libxml2 (?).

But maybe

I'm using
LIBXML_COMPILED_VERSION: (2, 9, 1)
LIBXML_VERSION: (2, 9, 1)
LIBXSLT_COMPILED_VERSION: (1, 1, 28)
LIBXSLT_VERSION: (1, 1, 28)
LXML_VERSION: (3, 4, 1, 0)
on Python 2.7

Holger

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