Python XML processing with lxml

Within an instance of this class, we keep one internal state item, the RelaxNG instance representing the .rng schema.

# - - - - -   c l a s s   R e l a x V a l i d a t o r

class RelaxValidator(object):
    '''Represents an XML validator for a given Relax NG schema.

      State/Invariants:
        .__schema:
          [ an etree.RelaxNG instance representing the effective schema ]
    '''