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.

def positions(self, account: str = '') -> List[Position]:
        """
        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.
        """
        if account:
            return list(self.wrapper.positions[account].values())
        else:
            return [v for d in self.wrapper.positions.values()
                    for v in d.values()]