How to check for change in the directory at FTP server?

Question

I want to get the file from FTP server to local as soon as new file is added in directory on FTP.

I know changes in the directory at local machine can be seen using watchdog observer.

But I want to check for the change in the directory (addition of new file, deletion on file) at FTP server.

How to achieve this?

Code I am using to check change in the directory on local machine:

from watchdog.observers import Observer
from watchdog.events import FileSystemEventHandler
import ftplib
import time

class ExampleHandler(FileSystemEventHandler):
    def on_created(self, event): 
        print "Got event for file %s" % event.src_path 

session = ftplib.FTP('address','username','password')
path='/directory/to/check'
session.cwd(path) 
observer = Observer()
event_handler = ExampleHandler() 
observer.schedule(event_handler, path_of_the_directory)
observer.start()
try:
    while True:
        time.sleep(1)
except KeyboardInterrupt:
    observer.stop()

observer.join()