code: def copy(self, source, dest):
          
          self._check_valid_key(source)
          self._check_valid_key(dest)
          return self._copy(source, dest)
docs: Copies a key. The destination is overwritten if does exist.
  
          :param source: The source key to copy
          :param dest: The destination for the copy
  
          :returns: The destination key
  
          :raises: exceptions.ValueError: If the source or target key are not valid
          :raises: exceptions.KeyError: If the source key was not found