[Tutor] Television simulation

[Dave Angel]

On 12/23/2011 04:43 PM, Dave Angel wrote:
> On 12/23/2011 04:21 PM, myles broomes wrote:
>> 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"
> The above line does nothing useful, as the value is thrown out when 
> the method returns.  Same is true in several other places below.
>>                          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.
>>
> Normally when such values are changed in the method, you want a 
> corresponding attribute of the instance to 'remember' the value.  In 
> your particular program you have one instance, called tv.  Each time 
> you call a method on that instance, such as tv.power_button(), you are 
> implicitly passing that instance to the method, as the value 'self'.  
> That's what you're not writing to correctly.
>
> Inside a method, you usually refer to such instance attributes as  
> self.attribname.  So let's try just one of them, the power button.
>
>         def power_button(self):
>                 if self.power == "off":
>                         self.power = "on"
>
>                       else:
>                                  self.power = 'off'
>                       print "Power is now ", self.power
>
> Notice I got rid of the unused parameter, since it was never referenced.
>
> One other thing we must do here:   In the __init__() method, you need 
> to initialize the state of the Television instance.  You can't just 
> print a statement saying it's initialized, you have to create each of 
> the attributes comprising its initial state.   In our case, we'd add a 
> line
>        self.power = "off"
>
>
> I'll leave the other two attributes to you.  There are other things I 
> could critique, but I want to give you the minimum push to make 
> something that could run.
>
Bah - It lined up when I typed it, but I pasted some of the original, 
and typed the rest.  Probably your email was html, when it should have 
been text.  Let's try again, indenting 4 spaces instead, a much more 
reasonable number than 8.

     def power_button(self):
         if self.power == "off":
             self.power = "on"
         else:
             self.power = "off"
         print "Power is now ", self.power


-- 

DaveA