#!/usr/bin/env python3

import json
import os
from itertools import chain, starmap

# Get the absolute path for the directory where this file is located "here"
here = os.path.abspath(os.path.dirname(__file__))

with open(os.path.join(here, "my.json")) as file:
    json_text = file.read()

json_data = json.loads(json_text)


def flatten_json_iterative_solution(dictionary):
    """Flatten a nested json file"""

    def unpack(parent_key, parent_value):
        """Unpack one level of nesting in json file"""
        # Unpack one level only!

        if isinstance(parent_value, dict):
            for key, value in parent_value.items():
                temp1 = parent_key + '_' + key
                yield temp1, value
        elif isinstance(parent_value, list):
            i = 0
            for value in parent_value:
                temp2 = parent_key + '_'+str(i)
                i += 1
                yield temp2, value
        else:
            yield parent_key, parent_value


    # Keep iterating until the termination condition is satisfied
    while True:
        # Keep unpacking the json file until all values are atomic elements (not dictionary or list)
        dictionary = dict(chain.from_iterable(starmap(unpack, dictionary.items())))
        # Terminate condition: not any value in the json file is dictionary or list
        if not any(isinstance(value, dict) for value in dictionary.values()) and \
           not any(isinstance(value, list) for value in dictionary.values()):
            break

    return dictionary

c = flatten_json_iterative_solution(json_data)

for k, v in c.items():
    print('set', k, v)

sever@sever:~/scripts/from-json-to-config$ ./test.py 
set high-availability_vrrp_group_BND028_advertise-interval 5
set high-availability_vrrp_group_BND028_interface eth1
set high-availability_vrrp_group_BND028_priority 250
set high-availability_vrrp_group_BND028_virtual-address 100.64.28.1/29
set high-availability_vrrp_group_BND028_vrid 28
set interfaces_ethernet_eth0_address 192.168.122.16/24
set interfaces_ethernet_eth0_description WAN
set interfaces_ethernet_eth0_hw-id 52:54:00:bf:fb:77
set interfaces_ethernet_eth1_hw-id 52:54:00:e8:86:f7
set system_config-management_commit-revisions 100
set system_console_device_ttyS0_speed 115200
set system_host-name r6-roll
set system_login_user_foo_authentication_encrypted-password $6$ertU59lKfma.gl91$vynXmhbee3GZF81zz4/z0
set system_login_user_vyos_authentication_encrypted-password $6$JkevvrMzWvcfM$pV9t/I16CEuhSp6ZYdzZUowg4ghl/yf/
set system_login_user_vyos_authentication_plaintext-password 
set system_login_user_vyos_authentication_public-keys_sever@sever_key AAAAB3NzaC1yc2EAAAADAQABAAABgQCj8sRksLQXSPk=
set system_login_user_vyos_authentication_public-keys_sever@sever_type ssh-rsa
set system_name-server_0 1.1.1.1
set system_name-server_1 8.8.8.8
set system_name-server_2 8.8.4.4
set system_syslog_global_facility_all_level info
set system_syslog_global_facility_protocols_level debug
set system_time-zone Europe/Kiev

set system_name-server_0 1.1.1.1
set system_name-server_1 8.8.8.8
set system_name-server_2 8.8.4.4