code: def from_etree(tree):
          
          exe = Executable(tree)
  
          exe.category = tree.findtext('category')
          exe.version = tree.findtext('version')
          exe.title = tree.findtext('title') or exe.name
          exe.description = tree.findtext('description')
          exe.license = tree.findtext('license') or "unknown"
          exe.contributor = tree.findtext('contributor')
  
          for ps in tree.iterfind("parameters"):
              assert isinstance(ps, ET.Element)
              paras = ParameterGroup(
                  ps.findtext("label"),
                  ps.findtext("description"),
                  ps.attrib.get('advanced', "false") == "true",
                  filter(lambda x: x is not None,
                         map(Parameter.from_xml_node, list(ps))))
  
              exe.parameter_groups.append(paras)
  
          return exe
docs: Constructs an executable form a given ElementTree structure.
  
          :param tree:
          :type tree: xml.etree.ElementTree.ElementTree
  
          :rtype: Executable