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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _WritePathInfo(self, client_id, path_info):
 """Writes a single path info record for given client."""

    if client_id not in self.metadatas:
      raise db.UnknownClientError(client_id)

    path_record = self._GetPathRecord(client_id, path_info)
    path_record.AddPathInfo(path_info)

    parent_path_info = path_info.GetParent()
    if parent_path_info is not None:
      parent_path_record = self._GetPathRecord(client_id, parent_path_info)
      parent_path_record.AddChild(path_info)