def max_last_string_column() -> int:
            """
            Returns:
                The max allowed width of the string value used for the last
                line we will construct.  Note that this value means the width
                rather than the number of characters (e.g., many East Asian
                characters expand to two columns).
            """
            result = self.line_length
            result -= line.depth * 4
            result -= 1 if ends_with_comma else 0
            result -= string_op_leaves_length
            return result

            Returns:
                The max allowed width of the string value used for the last
                line we will construct.  Note that this value means the width
                rather than the number of characters (e.g., many East Asian
                characters expand to two columns).
            
src/black/trans.py