[Tutor] Television simulation

[myles broomes]

Im trying to create a 'Television simulation' program. Heres the code ive written for it:

#television simulation
#a program that simulates a television
#the user can turn the television on or off, change the volume or change the channel

#create the television class
class Television(object):
        """A virtual television simulation"""
        def __init__(self):
                print("The television is off.")
		
        def power_button(self, power = "off"):
                if power == "off":
                        power = "on"
                        print("The power is now on.")
                else:
                        power = "off"
                        print("The power is now off.")
	
        def volume_button(self, volume = 0):
                up_or_down = input("Do you want to increase or decrease the volume? (up/down): ")
                if up_or_down == "up":
                        amount = int(input("By how much? (Enter a number): "))
                        volume += amount
                        if volume > 10:
                                volume = 10
                        print("The volume is now",volume)
                elif up_or_down == "down":
                        amount = int(input("By how much? (Enter a number): "))
                        volume += amount
                        if volume < 0:
                                volume = 0
                        print("The volume is now",volume)
                else:
                        print("That is not a valid choice.")
	
        def channel_button(self, channel = 1):
                new_channel = int(input("What channel do you want to watch? (Enter a number between 1 and 10.): "))
                if new_channel < 1 or new_channel > 10:
                        print("That is not a valid channel!")
                else:
                        channel = new_channel
                        print("The channel is now",channel)

#create the main part of the program, the television simulation
def main():
        tv = Television()

        choice = None
        while choice != "0":
                print \
                ("""
                Television simulation
	
                0 - Quit
                1 - Turn the television on or off
                2 - Change the volume
                3 - Change the channel
                """)
	
                choice = input("Choice: ")
                print()
	
                #exit
                if choice == "0":
                        print("Good-bye.")
		
                #turn the television on or off
                elif choice == "1":
                        tv.power_button()
	
                #increase or decrease the volume
                elif choice == "2":
                        tv.volume_button()
	
                #change the channel
                elif choice == "3":
                        tv.channel_button()
		
                else:
                        print("\nInvalid choice!")

main()
("\n\nPress the enter key to exit.")
			
		
It works fine but the problem im having is that when volume, channel or power are changed inside of their methods, their values dont change in the program if that makes sense. So i was just wondering if there was a way around this. 

Thanks in advance,
Myles Broomes