code: def read_keys(self, keys, dict_cls=AttrDict, path="/"):
          
          od = dict_cls()
          for k in keys:
              try:
                  # Try to read a variable.
                  od[k] = self.read_value(k, path=path)
              except self.Error:
                  try:
                      # Try to read a dimension.
                      od[k] = self.read_dimvalue(k, path=path)
                  except self.Error:
                      od[k] = None
  
          return od
docs: Read a list of variables/dimensions from file. If a key is not present the corresponding
          entry in the output dictionary is set to None.