How to use the napalm.base.exceptions.MergeConfigException function in napalm

+ self._BACKUP_FILENAME)
                    self._new_config = f.read()
                    cfg = [x for x in self._new_config.split("\n") if x is not ""]
                    output_loadcmd = self.device.send_config_set(cfg)
                    match_setfailed = re.findall("Delete failed", output_loadcmd)
                    match_delfailed = re.findall("Set failed", output_loadcmd)

                    if match_setfailed or match_delfailed:
                        raise MergeConfigException("Failed merge config: "
                                                   + output_loadcmd)
            else:
                raise MergeConfigException("config file is not found")
        elif config is not None:
            self._new_config = config
        else:
            raise MergeConfigException("no configuration found")

elif "%Please turn config archive on" in output:
                msg = "napalm-ios replace() requires Cisco 'archive' feature to be enabled."
                raise ReplaceConfigException(msg)
        else:
            # Merge operation
            filename = self.merge_cfg
            cfg_file = self._gen_full_path(filename)
            if not self._check_file_exists(cfg_file):
                raise MergeConfigException("Merge source config file does not exist")
            cmd = "copy {} running-config".format(cfg_file)
            output = self._commit_handler(cmd)
            if "Invalid input detected" in output:
                self.rollback()
                err_header = "Configuration merge failed; automatic rollback attempted"
                merge_error = "{0}:\n{1}".format(err_header, output)
                raise MergeConfigException(merge_error)

        # After a commit - we no longer know whether this is configured or not.
        self.prompt_quiet_configured = None

        # Save config to startup (both replace and merge)
        output += self.device.save_config()

def load_merge_candidate(self, filename=None, config=None):
        """
        SCP file to remote device.

        Merge configuration in: copy  running-config
        """
        self.config_replace = False
        return_status, msg = self._load_candidate_wrapper(
            source_file=filename,
            source_config=config,
            dest_file=self.merge_cfg,
            file_system=self.dest_file_system,
        )
        if not return_status:
            raise MergeConfigException(msg)

output = ''

        try:
            output += self.device.send_command('system-view', expect_string=r'\[.+\]')
            for command in commands:
                output += self.device.send_command(command, expect_string=r'\[.+\]')

            if self.device.check_config_mode():
                check_error = re.search("error", output, re.IGNORECASE)
                if check_error is not None:
                    return_log = self.device.send_command('return', expect_string=r'[<\[].+[>\]]')
                    if 'Uncommitted configurations' in return_log:
                        # Discard uncommitted configuration
                        return_log += self.device.send_command('n', expect_string=r'<.+>')
                    output += return_log
                    raise MergeConfigException('Error while applying config!')
                output += self.device.send_command('commit', expect_string=r'\[.+\]')
                output += self.device.send_command('return', expect_string=r'<.+>')
            else:
                raise MergeConfigException('Not in configuration mode.')
        except Exception as e:
            msg = str(e) + '\nconfiguration output: ' + output
            raise MergeConfigException(msg)

commands = self._multiline_convert(commands, start=start, depth=depth)

        commands = self._mode_comment_convert(commands)

        try:
            if self.eos_autoComplete is not None:
                self.device.run_commands(commands, autoComplete=self.eos_autoComplete)
            else:
                self.device.run_commands(commands)
        except pyeapi.eapilib.CommandError as e:
            self.discard_config()
            msg = str(e)
            if replace:
                raise ReplaceConfigException(msg)
            else:
                raise MergeConfigException(msg)

def _commit_merge(self):
        try:
            output = self._send_config(self.merge_candidate)
            if output and "Invalid command" in output:
                raise MergeConfigException("Error while applying config!")
        except Exception as e:
            self.changed = True
            self.rollback()
            err_header = "Configuration merge failed; automatic rollback attempted"
            merge_error = "{0}:\n{1}".format(err_header, repr(str(e)))
            raise MergeConfigException(merge_error)

        self.changed = True
        # clear the merge buffer
        self.merge_candidate = ""

for command in commands:
                output += self.device.send_command(command, expect_string=r'\[.+\]')

            if self.device.check_config_mode():
                check_error = re.search("error", output, re.IGNORECASE)
                if check_error is not None:
                    return_log = self.device.send_command('return', expect_string=r'[<\[].+[>\]]')
                    if 'Uncommitted configurations' in return_log:
                        # Discard uncommitted configuration
                        return_log += self.device.send_command('n', expect_string=r'<.+>')
                    output += return_log
                    raise MergeConfigException('Error while applying config!')
                output += self.device.send_command('commit', expect_string=r'\[.+\]')
                output += self.device.send_command('return', expect_string=r'<.+>')
            else:
                raise MergeConfigException('Not in configuration mode.')
        except Exception as e:
            msg = str(e) + '\nconfiguration output: ' + output
            raise MergeConfigException(msg)

("original configuration has been successfully restored" in output)
                or ("error" in output.lower())
                or ("not a valid config file" in output.lower())
                or ("failed" in output.lower())
            ):
                msg = "Candidate config could not be applied\n{}".format(output)
                raise ReplaceConfigException(msg)
            elif "%Please turn config archive on" in output:
                msg = "napalm-ios replace() requires Cisco 'archive' feature to be enabled."
                raise ReplaceConfigException(msg)
        else:
            # Merge operation
            filename = self.merge_cfg
            cfg_file = self._gen_full_path(filename)
            if not self._check_file_exists(cfg_file):
                raise MergeConfigException("Merge source config file does not exist")
            cmd = "copy {} running-config".format(cfg_file)
            output = self._commit_handler(cmd)
            if "Invalid input detected" in output:
                self.rollback()
                err_header = "Configuration merge failed; automatic rollback attempted"
                merge_error = "{0}:\n{1}".format(err_header, output)
                raise MergeConfigException(merge_error)

        # After a commit - we no longer know whether this is configured or not.
        self.prompt_quiet_configured = None

        # Save config to startup (both replace and merge)
        output += self.device.save_config()