code: def positions(self, account: str = '') -> List[Position]:
          
          if account:
              return list(self.wrapper.positions[account].values())
          else:
              return [v for d in self.wrapper.positions.values()
                      for v in d.values()]
docs: List of positions for the given account,
          or of all accounts if account is left blank.
  
          Args:
              account: If specified, filter for this account name.