Tkinter: instances in init are not recognised

Question

I have this code, in which pressing each one of three buttons, label2 text should record their state.

from Tkinter import *

class App:

    def __init__(self, master):

        self.state = [False, False, False]
        frame = Frame(master)
        frame.pack()

        self.label1 = Label(frame, text="buttons", fg="black").grid(row=0)
        self.buttonR = Button(frame, text="RED", fg="red", command=self.controlR).grid(row=1, column=0)
        self.buttonG = Button(frame, text="GREEN", fg="green", command=self.controlG).grid(row=1, column=1)
        self.buttonB = Button(frame, text="BLUE", fg="blue", command=self.controlB).grid(row=1, column=2)
        self.label2 = Label(frame, text="results", fg="black").grid(row=2)

    def controlR(self):
        self.state[0] = not self.state[0]
        self.results()
    def controlG(self):
        self.state[1] = not self.state[1]
        self.results()
    def controlB(self):
        self.state[2] = not self.state[2]
        self.results()

    def results(self):
        color_list = ["RED", "GREEN", "BLUE"]
        my_str = 'button '
        for i in xrange(len(color_list)):
            my_str += color_list[i]
            if self.state[i] == False:
                my_str += " is OFF \n"
            else:
                my_str += " is ON \n"    
        print my_str
        print type(self.label2)  
        self.label2['text'] = my_str

root = Tk()
app = App(root)
root.mainloop()
root.destroy()

What I get is TypeError: 'NoneType' object does not support item assignment because each one of the five widgets launched in the init definition are not recognized as instances in the results definition. Thus print type(self.label2) returns NoneType.

Why does it happen? Any thoughts would be appreciated.

score 2 · Accepted Answer · answered Oct 10 '16 at 07:15

It's because in this section of your code:

self.label1 = Label(frame, text="buttons", fg="black").grid(row=0)
self.buttonR = Button(frame, text="RED", fg="red", command=self.controlR).grid(row=1, column=0)
self.buttonG = Button(frame, text="GREEN", fg="green", command=self.controlG).grid(row=1, column=1)
self.buttonB = Button(frame, text="BLUE", fg="blue", command=self.controlB).grid(row=1, column=2)
self.label2 = Label(frame, text="results", fg="black").grid(row=2)

You're assigned the result of calling the grid() method of the widgets, and it returns 'None'. To prevent this, just do something like this with each one of them instead:

self.label1 = Label(frame, text="buttons", fg="black")
self.label1.grid(row=0)

Tkinter: instances in __init__ are not recognised

1 Answers1

Tkinter: instances in init are not recognised