Python signal when a variable changes?

Question

I have a script that calculates a variable every second (my program reads the output of the script bash and interprets the data every second). Is there a way to detect if this var has changed?

Here is part of my code, the text is ffmpeg or avconv output read from vte terminal:

#Terminal
def terminal(self):
        self.v = vte.Terminal()
        self.v.connect ("child-exited", lambda term: self.verif(self, my_class))
        self.v.connect('contents-changed', self.term_output)
        [...]    
def term_output(self, my_class, donnees=None):
        text = str(self.v.get_text(lambda *a: True).rstrip())
        [...] # decode the text
        print "time", self.time
        print "duration", self.duration

Return in vte terminal (avconv output):

Duration: 00:00:23.00, start: 0.100511, bitrate: 0 kb/s
Output #0, matroska, to '/media/guillaume/XT/Telechargements/uzz/la_qualite_de_l_air_1000019643.mkv':
Press [q] to stop, [?] for help
frame=  589 fps=115 q=-1.0 Lsize=    2191kB time=00:00:23.79 bitrate= 754.3kbits/s
FIN DU TRAITEMENT
Votre Fichier Final Est:
/media/guillaume/XT/Telechargements/uzz/la_qualite_de_l_air_1000019643.mkv

Output example (vte output time and duration):

time 5.1
duration 23.0
time 6.1
duration 23.0
time 9.1
duration 23.0
time 14.1
duration 23.0
time 14.1
duration 23.0
time 16.1
duration 23.0
time 18.1
duration 23.0
time 19.1
duration 23.0
time 21.1
duration 23.0
time 23.1
duration 23.0
time 23.1
duration 23.0
time 23.1
duration 23.0
time 23.1
duration 23.0
time 23.1
duration 3960.0 # detect this change? (correspond to a second output of avconv)
time 1.1
duration 3960.0
time 7.1
duration 3960.0
time 10.1
duration 3960.0
time 20.1
duration 3960.0
time 20.1
duration 3960.0 

Answer 1

Add a flag variable (global or local, depending on the required area).

Assign a value to the flag at the start / first loop.

Compare the value of this flag with the variable and, if it changes, (either a signal or print what you need).

time_val = 'init';

def term_output(self, my_class, donnees=None):
    text = str(self.v.get_text(lambda *a: True).rstrip())
    [...] # decode the text
    if (time_val == 'init'):
        time_val = self.time
    if self.time != time_val:
        print "The value of time has changed from " + str(time_val) + " to " + str(self.time)
    print self.time