Dynamic Class Creation

Wed Mar 17 04:54:14 EDT 2010

Josh English wrote:
> Chris,
>> Thanks. This worked for the attributes, but I think the tactic is
> still misleading. There are child elements I can't quite determine how
> to deal with:
>> <market code='anlg' tier='ProMarket' mail='True'>
> <title field="pref">Analog Science Fiction and Fact</title>
> <nickname>Analog</nickname>
> <keyword>Science Fiction</keyword>
> <keyword>First Contact</keyword>
> <keyword>Hard Science Fiction</keyword>
> <address>
> <attnline>Stanley Schmidt, Editor</attnline>
> <address1>267 Broadway, 4th Floor</address1>
> <address2>New York, NY 10007-2352</address2>
> </address>
> <website>http://www.analogsf.com</website>
> </market>
>> A child element with text and an attribute or two, for example, pose a
> problem. I can call Market.title but should I try Market.title.field
> or Market.title_field.
>> Multiple elements, such as keywords, are allowed in xml but harder to
> map to the object. I don't know if I want to go create a list and
> methods for accessing those keywords as a list, or redefine the rules
> of my XML to not allow multiple child elements with the same tag. I
> can't decide.
>> Then the address is a bit of a bear.
>> In short, I have to figure out the whole object interface to the XML
> and how I want that to work.
>
Have you heard of or considered PyXB (http://pyxb.sourceforge.net/)? Not 
that I've much experience with it, but you can use it to generate python 
code from XML Schema files, and, I think, WSDL definitions. It's a bit 
of a rabbit hole, but then isn't that half the fun!
The following might give you the idea. You start with a Schema 
schema.xsd, generate a python module from it, then read in some XML with 
the generated classes to get your custom objects.
---------------- schema.xsd ----------------------
<xs:schema targetNamespace="http://www.josh.com/schema/0.1"
 xmlns:xs="http://www.w3.org/2001/XMLSchema"
 xmlns:josh="http://www.josh.com/schema/0.1">
 <xs:element name="market" type="josh:MarketType"/>
 <xs:complexType name="MarketType">
 <xs:sequence>
 <xs:element name="title" type="josh:TitleType"/>
 <xs:element name="nickname" type="xs:string"/>
 <xs:element name="keyword" type="xs:string" 
maxOccurs="unbounded"/>
 <xs:element name="address" type="josh:USAddress"/>
 <xs:element name="website" type="xs:string"/>
 </xs:sequence>
 <xs:attributeGroup ref="josh:MarketAttributes"/>
 </xs:complexType>
 <xs:complexType name="TitleType">
 <xs:simpleContent>
 <xs:extension base="xs:string">
 <xs:attribute name="field" type="xs:string"/>
 </xs:extension>
 </xs:simpleContent>
 </xs:complexType>
 <xs:attributeGroup name="MarketAttributes">
 <xs:attribute name="code" type="xs:string"/>
 <xs:attribute name="tier" type="xs:string"/>
 <xs:attribute name="mail" type="xs:string"/>
 </xs:attributeGroup>
 <xs:complexType name="Address" abstract="true">
 <xs:sequence>
 <xs:element name="name" type="xs:string"/>
 <xs:element name="street" type="xs:string"/>
 <xs:element name="city" type="xs:string"/>
 </xs:sequence>
 </xs:complexType>
 <xs:complexType name="USAddress">
 <xs:complexContent>
 <xs:extension base="josh:Address">
 <xs:sequence>
 <xs:element name="state" type="josh:USState" 
minOccurs="0"/>
 <xs:element name="zip" type="xs:positiveInteger" 
minOccurs="0"/>
 </xs:sequence>
 </xs:extension>
 </xs:complexContent>
 </xs:complexType>
 <xs:simpleType name="USState">
 <xs:restriction base="xs:string">
 <xs:enumeration value="AK"/>
 <xs:enumeration value="AL"/>
 <xs:enumeration value="AR"/>
 <!-- and so on ... -->
 </xs:restriction>
 </xs:simpleType>
</xs:schema>
---------------- genbindings.sh ---------------------------
#!/bin/sh
pyxbgen -u schema.xsd -m market_binding -r
---------------- demo.py -----------------------------------
s = """<?xml version="1.0"?>
<josh:market
 xmlns:josh="http://www.josh.com/schema/0.1"
 code="anlg"
 tier="ProMarket"
 mail="True">
 <title field="pref">Analog Science Fiction and Fact</title>
 <nickname>Analog</nickname>
 <keyword>Science Fiction</keyword>
 <keyword>First Contact</keyword>
 <keyword>Hard Science Fiction</keyword>
 <address>
 <name>Stanley Schmidt, Editor</name>
 <street>267 Broadway, 4th Floor</street>
 <city>New York</city>
 </address>
 <website>http://www.analogsf.com</website>
</josh:market>
"""
import xml.dom.minidom
import market_binding
market = 
market_binding.CreateFromDOM(xml.dom.minidom.parseString(s).documentElement)
print market.tier
print market.code
print market.keyword
assert len(market.keyword) == 3
print market.address.name
print market.toxml()