Return a string summary of transaction

def summary(self):
        """Return a string summary of transaction"""
        return "\n".join([
            "Transaction:",
            "  When:        " + self.date.strftime("%a %d %b %Y"),
            "  Description: " + self.desc.replace('\n', ' '),
            "  For amount:  {}".format(self.amount),
            "  From:        {}".format(
                ", ".join(map(lambda x: x.account, self.src)) if self.src \
                    else "UNKNOWN"
            ),
            "  To:          {}".format(
                ", ".join(map(lambda x: x.account, self.dst)) if self.dst \
                    else "UNKNOWN"
            ),
            ""
        ])