code: def Prepend(self, **kw):
          kw = copy_non_reserved_keywords(kw)
          for key, val in kw.items():
              try:
                  orig = self._dict[key]
              except KeyError:
                  self._dict[key] = val
              else:
                  try:
                      update_dict = orig.update
                  except AttributeError:
                      try:
                          self._dict[key] = val + orig
                      except (KeyError, TypeError):
                          try:
                              add_to_val = val.append
                          except AttributeError:
                              if val:
                                  orig.insert(0, val)
                          else:
                              if orig:
                                  add_to_val(orig)
                              self._dict[key] = val
                  else:
                      if SCons.Util.is_List(val):
                          for v in val:
                              orig[v] = None
                      else:
                          try:
                              update_dict(val)
                          except (AttributeError, TypeError, ValueError):
                              if SCons.Util.is_Dict(val):
                                  for k, v in val.items():
                                      orig[k] = v
                              else:
                                  orig[val] = None
          self.scanner_map_delete(kw)