Return string with data in tabular form.

def to_table(self, filter_function=None):
        """Return string with data in tabular form."""
        table = []
        for p in self:
            if filter_function is not None and filter_function(p): continue
            table.append([p.basename, p.symbol, p.Z_val, p.l_max, p.l_local, p.xc, p.type])
        return tabulate(table, headers= ["basename", "symbol", "Z_val", "l_max", "l_local", "XC", "type"],
                        tablefmt="grid")