code: def exists(self, root):
          
          for node in root.children:
              if node.name != 'import':
                  continue
              ns = node.get('namespace')
              if self.ns == ns:
                  return 1
          return 0
docs: Check to see if the <xs:import/> already exists
          in the specified schema root by matching I{namesapce}.
          @param root: A schema root.
          @type root: L{Element}