code: def iter_chain(cur):
      
      select = "SELECT nodes FROM chain"
      for nodes, in cur.execute(select):
          yield json.loads(nodes)
docs: Iterate over all of the chains in the database.
  
      Args:
          cur (:class:`sqlite3.Cursor`):
              An sqlite3 cursor. This function is meant to be run within a :obj:`with` statement.
  
      Yields:
          list: The chain.