code: def genPrefixes(self):
          
          prefixes = {}
          n = 0
          for u in self.namespaces:
              p = 'ns%d' % n
              prefixes[u] = p
              n += 1
          return prefixes
docs: Generate a I{reverse} mapping of unique prefixes for all namespaces.
          @return: A referse dict of prefixes.
          @rtype: {u, p}