from gi.repository import Notify
import time
Notify.init('Python')

def progress(i=1):
    assert(i <= 10)
    return '[{0:10}]'.format('#' * i)

n = Notify.Notification.new("Volume", progress(1), 'volume')
n.show()

for i in range(2, 11):
    time.sleep(0.5)
    n.update("Volume", progress(i), 'volume')
    n.show()
