input

[{
  "longitude":51.5074,
  "latitude":0.1278
}]

output

[{
  "longitude":51.5074,
  "latitude":0.1278
},
  "longitude":51.5074,
  "latitude":0.1278
}]

script.py

    latlong = { "latitude": latitude,"longitude": longitude}
    
    
    
    ##first time run
    if os.stat(filepath).st_size==0: //check to see if file has been created if not, write first line.
        with open(filepath, 'w') as outfile:
            json.dump(latlong, outfile)
    else:
    ##apending the json dict
        with open(filepath, mode='r+') as feedsjson:  //this is where the file is meant to be appended.
            feeds = json.load(feedsjson)
            newdata = (latlong)
            feeds.update(newdata)
            json.dump(feeds, feedsjson)