How do you poll for changes in a JSON file using a python script that runs in the background and extract the changes?

Question

I have a JSON file that is placed in the /etc/ folder of a Linux system and contains the properties of a Router. Lets say the user wants to change the configuration of the Router and changes the IP of an interface. I am working on a python script that keeps polling the file for changes in the JSON file and extract the new data that has changed for further processing.

"device": 
            {
                "device_image": "", 
                "password": "", 
                "interface": [
                    {
                        "interface_ip": "", 
                        "interface_type": "", 
                        "interface_name": "", 
                        "interface_uid": ""
                    }, 
                    {
                        "interface_ip": "", 
                        "interface_type": "", 
                        "interface_name": "", 
                        "interface_uid": ""
                    }, 
                    {
                        "interface_ip": "", 
                        "interface_type": "", 
                        "interface_name": "", 
                        "interface_uid": ""
                    }, 
                    {
                        "interface_ip": "", 
                        "interface_type": "", 
                        "interface_name": "", 
                        "interface_uid": ""
                    }
                ], 
                "username": "", 
                "device_id": "", 
                "ipaddress": "", 
                "gateway": "", 
                "device_name": "R1"
            }

Is there a easy way to do this?

Answer 1

A loop opening the file and cheking for differences should work:

from time import sleep
from os import listdir

sleeptime = 5

if "old_json.json" in listdir("/path/"):
    with open("/path/old_json.json/", "r") as f: old_json = f.read()

else:
    with open("/path/json.json/", "r") as f: old_json = f.read()


while True:
    with open("/path/json.json/", "r") as f: json = f.read()
    if json != old_json:
        print "json changed!"

    old_json = json

    with open("/path/old_json.json/", "w") as f: f.write(old_json)

    sleep(sleeptime)

sleeptime is in seconds