TypeError: on_current_bg() takes 1 positional argument but 3 were given

[Glen Rubin]

Hi Friends!

I'm having issues with and on_ type property method.  

I have a string property called current_bg and want to implement on_current_bg so that some functions are called whenever current_bg is updated.  When my program runs I get the error in the subject line:

 TypeError: on_current_bg() takes 1 positional argument but 3 were given

Here is a minimal version of my program:

from kivy.uix.screenmanager import Screen
from kivy.properties import StringProperty, ListProperty, NumericProperty

class SweetLight(Screen):
    #property list
    current_bg = StringProperty('')
    label_color = ListProperty([0, 0, 0, 1])
    R = NumericProperty(0)
    G = NumericProperty(0)
    B = NumericProperty(0)
    A = NumericProperty(1)

    def on_pre_enter(self):
        self.current_bg = self.manager.current_bg

    def on_current_bg(self):
        self.RGB(int(self.current_bg))

    def RGB(self, bg):
        self.bg2R(bg)
        self.bg2G(bg)
        self.bg2B(bg)

    def bg2R(self, bg):
        R=2
        self.R = R
        self.label_color[0] = R / 255.0

    def bg2G(self, bg):
        G= 100
        self.G = G
        self.label_color[1] = G / 255.0

    def bg2B(self, bg):
        B=155
        self.B = B
        self.label_color[2] = B / 255.0

[Elliot Garbus]

See: https://kivy.org/doc/stable/api-kivy.properties.html?highlight=properties#observe-using-on-propname

When the kivy property changes  self, instance and value are passed to the event handler.

 

The python convention is the use CapWords for classes and snake_case for methods.  You might want to change the method RGB to rgb

See: https://pep8.org/#class-names

 

Im not sure what you are trying to do – but you might find some of the utils helpful:  https://kivy.org/doc/stable/api-kivy.utils.html?highlight=utils#kivy.utils.rgba

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[Glen Rubin]

awesome, thanks for the tip!  I might be able to use that util to shrink my code :D

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