python: how to define types for conversion to xml

Question

I am implementing a parser in python 2.7 for an xml-based file format. The format defines classes with fields of specific types.

What I want to do is define objects like this:

class DataType1(SomeCoolParent):
    a = Integer()
    b = Float()
    c = String()
    #and so on...

• The resulting classes need to be able to be constructed from an XML document, and render back into XML (so that I can save and load files).

• This looks a whole lot like the ORM libraries in SQLAlchemy or Django... except that there is no database, just XML. It's not clear to me how I would implement what I'm after with those libraries. I would basically want to rip out their backend database stuff and have my own conversion to XML and back again.

• My current plan: set up a metaclass and a parent class (SomeCoolParent), define all the types (Integer, Float, String), and generally build a custom almost-ORM myself. I know how to do this, but it seems that someone else must have done/thought of this before, and maybe come up with a general-purpose solution...
• Is there a "better" way to implement a hierarchy of fixed type structures with python objects, which allows or at least facilitates conversion to XML?

Caveats/Notes

• As mentioned, I'm aware of SQLAlchemy and Django, but I'm not clear on how/whether I can do what I want with their ORM libraries. Answers that show how to do this with either of them definately count.
• I'm definitely open to other methods, those two are just the ORM libraries I am aware of.

Answer 1

There a several XML Schema specifications out there. My knowledge is somewhat dated but XML Schema (W3C) - a.k.a. XSD and relax ng are the most popular with relax ng having a lower learning curve. With that in mind, a good ORM (or would that be OXM 'Object-XML Mapper) using these data description formats ought to be out there. Some candidates are

• pyxb
• generateDS

Stronger google foo may yield more options.