def check_certs(self, key_file, cert_file):
        # TODO: maybe validate these? wrap_socket doesn't...

        if not os.path.exists(key_file):
            raise CommandError(key_file % "Can't find key at %s")
        if not os.path.exists(cert_file):
            raise CommandError("Can't find certificate at %s" %
                               cert_file)
dataset/ETHPy150Open teddziuba/django-sslserver/sslserver/management/commands/runsslserver.py/Command.check_certs/swapped operands of `%`