Python, handling multiple values from an index

[Dujith]

I'm trying to figure out something in python.

Programming a Homeserver to make 1 module that will handle converting RGB to xy

The problem i am running into is the way i have to input values and they dont seem to stay in memory.

 

      if index == 2 or index == 3 or index == 4:
              
        if index == 2:
          rgbrood = value
        elif index == 3:
          rgbgroen = value
        else:
          rgbblauw = value
      
      #Caculate RGB -> xy
      print ('pre temp')
      temp = (rgbrood+rgbgroen+rgbrood)
      print ('after temp')
      print (temp)  

In the homeserver i define an object which has any number of inputs. whenever an input changes it will trigger: def on_input_value(self, index, value):

The index is my input number and from it i can get a value (1 is my on/off and 5 is my brightness, those work)

When i run this it will stop at my debug print (pre temp) and will stop there. 

 

I started using python 2.7 this week and was able to fix many things by searching and watching youtube, but this has me stumped atm. 

I'm prob doing something very stupid and will be happy to hear how stupid  

[79wjd]

rgbrood, rgbroen, rgbblauw are attributes of a class? Then do self.rgbrood = value etc... as you want to change the object's attribute, not define a new variable that happens to share the same name as one of the class's attributes.

[Dujith]

15 minutes ago, 79wjd said:

rgbrood, rgbroen, rgbblauw are attributes of a class? Then do self.rgbrood = value etc... as you want to change the object's attribute, not define a new variable that happens to share the same name as one of the class's attributes.

they are new, and were meant to hold the values so i can calculate with them.

[Dujith]

      if index == 2 or index == 3 or index == 4:
              
        if index == 2:
          rgbrood = 1
        elif index == 3:
          rgbgroen = 2
        else:
          rgbblauw = 3
      
      #Caculate RGB -> xy
      print ('pre temp')
      print (rgbrood)
      print ('after temp')

If i simplify the code i notice something

setting the index 2 value to 1 will set rgbrood to 1 as seen in that statement and it will print the value

However if i then set a value to the 3rd index it will no longer print the value of rgbrood ? so its volatile?

[79wjd]

9 minutes ago, Dujith said:

      if index == 2 or index == 3 or index == 4:
              
        if index == 2:
          rgbrood = 1
        elif index == 3:
          rgbgroen = 2
        else:
          rgbblauw = 3
      
      #Caculate RGB -> xy
      print ('pre temp')
      print (rgbrood)
      print ('after temp')

If i simplify the code i notice something

setting the index 2 value to 1 will set rgbrood to 1 as seen in that statement and it will print the value

However if i then set a value to the 3rd index it will no longer print the value of rgbrood ? so its volatile?

Yes, it's volatile and will be lost as soon as it goes out of scope -- which it will once you leave the function.

[Dujith]

4 minutes ago, 79wjd said:

Yes, it's volatile and will be lost as soon as it goes out of scope -- which it will once you leave the function.

So whats normally used for storing values?

[Dujith]

@79wjd

Found it, need to set a global variable and call it as such

        if index == 2:
          global rgbrood
          rgbrood = 1

Thanks for pointing me in the correct direction  i mean it btw, sometimes i just need key words and scope - variable did it for me.

[79wjd]

2 hours ago, Dujith said:

@79wjd

Found it, need to set a global variable and call it as such

        if index == 2:
          global rgbrood
          rgbrood = 1

Thanks for pointing me in the correct direction  i mean it btw, sometimes i just need key words and scope - variable did it for me.

Glad to help.

 

It's fine to use globals, but there is usually a better solution. Globals are often used as a hacky solution to get around scope issues that were designed to exist for a reason. That's not to say you should never use globals, but it's not a bad habit to be in to design solutions that don't rely on them.

 

In this particular case, it would seem reasonable for those to be members of the class. Although, that is without having seen any of the code.