[Tutor] automatic setting of class property when another one changes

[ingo]

Rather stuck with this one, I'd like to automatically (re)set the 
propery "relaystate" when one of the others (Tm, Tset, Th) is set, 
regardless of wether their value has changed.

Ingo

My code so far:

from collections import namedtuple
import logging

logger = logging.getLogger()
logger.setLevel(logging.DEBUG)
stream_handler = logging.StreamHandler()
stream_handler.setLevel(logging.DEBUG)
formatter = logging.Formatter(
     '[%(levelname)-8s] %(asctime)s (%(name)-8s) - %(message)s',
     '%Y-%m-%d %H:%M:%S',
)
stream_handler.setFormatter(formatter)
logger.addHandler(stream_handler)


class Thermostat():
     def __init__(self, Tm=20, Tset=20, Th=0.3):
         logger.debug("__INIT__")
         self.Tm = Tm
         self.Tset = Tset
         self.Th = Th
         self.relaystate = None

     @property
     def Tm(self):
         logger.debug("GETTER Tm")
         return self._Tm
     @Tm.setter
     def Tm(self, value):
         logger.debug("SETTER Tm")
         self._Tm = value

     @property
     def Tset(self):
         logger.debug("GETTER Tset")
         return self._Tset
     @Tset.setter
     def Tset(self, value):
         logger.debug("SETTER Tset")
         self._Tset = value

     @property
     def Th(self):
         logger.debug("GETTER Th")
         return self._Th
     @Th.setter
     def Th(self, value):
         logger.debug("SETTER Th")
         self._Th = value

     @property
     def relaystate(self):
         logger.debug("GETTER relaystate")
         return self._relaystate
     @relaystate.setter
     def relaystate(self, value):
         logger.debug("SETTER relaystate")
         #on init while setting Tm, Tset and Th are not known
         #so relaystate can not be calculated
         try:
             lower = self.Tset-self.Th
             upper = self.Tset+self.Th
         except AttributeError as e:
             logger.debug("SETTER relaystate : %s", e)
             self._relaystate = None
         rlstate = namedtuple('relaystate', ['heat', 'cool'])
         if self.Tm < lower:
             value = rlstate(1,0)
         elif self.Tm > upper:
             value = rlstate(0,1)
         elif self.Tm > lower and self.Tm < upper:
             value = rlstate(0,0)
         self._relaystate = value


if __name__ == "__main__":

     TS1 = Thermostat()
     TS1.Tset = 44
     print("heat : ",TS1.relaystate.heat,"cool : ",TS1.relaystate.cool)