Problem with tkinter checkbutton and class

Question

I have some problems with Checkbutton in classes. They always return the start value. I am attaching the example code, in Main.py I create a window and a button to invoke my class with the checkbutton. In this second class (WindowProteins.py:) the check button does not work and always returns the same value

Main.py:

#tkinter import
import tkinter as tk
from tkinter import *
from tkinter import filedialog
from tkinter.filedialog import askopenfile
from tkinter.messagebox import showinfo

import WindowProteins as wPr

#font
font_title = ('times', 18, 'bold')
font_subtitle = ('times', 14, 'bold')

def CreateProteins():
   windowPr = wPr.ProteinsWindow()
   windowPr.mainloop()

#create welcome window
def CreateWelcome():
   #window
   global window_welcome
   window_welcome = tk.Tk()
   window_welcome.geometry("400x300")  # Size of the window 
   window_welcome.title('Main')
   #button
   btn_proteins = tk.Button(window_welcome, text='Proteins', 
      width=20,command = lambda:CreateProteins())
   btn_proteins.grid(row=2,column=1)

   window_welcome.mainloop()  #Keep the window open

CreateWelcome()

WindowProteins.py:

#tkinter import
import tkinter as tk
from tkinter import *
from tkinter import filedialog
from tkinter.filedialog import askopenfile
from tkinter.messagebox import showinfo

class ProteinsWindow(tk.Tk):
  df = pd.DataFrame()

  def __init__(self):
    super().__init__()

    # configure the root window
    self.title('Proteins')
    self.geometry('800x400')

    #fonts
    self.font_title=('times', 18, 'bold')
    self.font_subtitle = ('times', 14, 'bold')
    self.font_base = ('times', 11)

    #Protein FDR checkboxes
    self.var_chc_low = IntVar(value=1)
    self.chc_low = tk.Checkbutton(self, text='Low',variable=self.var_chc_low, onvalue=1, offvalue=0, command=self.agreement_changed )
    self.chc_low.grid(row=0,column=0, sticky='w')
    self.chc_low.select()

  def agreement_changed(self):
     print(str(self.var_chc_low.get()))

how can i solve?

You have multiple instances of Tk() here - an explicit one in CreateWelcome(), and as the base class of ProteinsWindow. One of the numerous problems caused by this is that Tkinter Vars don't work right. Use Toplevel instead as the base class for your second window. — jasonharper
– jasonharper, Commented Aug 18, 2022 at 13:46
Thanks for the reply! I am quite new to python, could you explain better what you mean please? — Mario
– Mario, Commented Aug 18, 2022 at 13:53
you should use tk.Tk() only to create main window. Other windows you should create using tk.Toplevel(). And you should use only one mainloop() because two loops can make conflict when you try to get value. — furas
– furas, Commented Aug 18, 2022 at 14:11
shorter: command=CreateProteins without lambda and without () (and without spaces around = - see more PEP 8 -- Style Guide for Python Code ) — furas
– furas, Commented Aug 18, 2022 at 14:12
Perfect now everything works, thank you very much! If you create an answer I can accept it — Mario
– Mario, Commented Aug 18, 2022 at 14:18

furas · Accepted Answer · 2022-08-18 14:26:57Z

You should use tk.Tk() only to create main window. Other windows you should create using tk.Toplevel(). And you should use only one mainloop() because two loops (and two main windows) can make conflict when you try to get value.

Working code (as single file) with other changes

You may use BooleanVar() and True/False instead of IntVar() and 1/0

import tkinter as tk  # PEP8: `import *` is not preferred
from tkinter import filedialog
from tkinter.filedialog import askopenfile
from tkinter.messagebox import showinfo
import pandas as pd

# font
font_title = ('times', 18, 'bold')
font_subtitle = ('times', 14, 'bold')

# --- classes ---  # PEP8: `CamelCaseNames`

class ProteinsWindow(tk.Toplevel):

    def __init__(self):
        super().__init__()

        self.df = pd.DataFrame()
     
        # configure the root window
        self.title('Proteins')
        self.geometry('800x400')

        # fonts
        self.font_title = ('times', 18, 'bold')
        self.font_subtitle = ('times', 14, 'bold')
        self.font_base = ('times', 11)

        # Protein FDR checkboxes
        self.var_chc_low = tk.BooleanVar(value=True)
        self.chc_low = tk.Checkbutton(self, text='Low', variable=self.var_chc_low, onvalue=True, offvalue=False, command=self.agreement_changed)
        self.chc_low.grid(row=0, column=0, sticky='w')
        self.chc_low.select()

    def agreement_changed(self):
        print(self.var_chc_low.get())

# --- functions ---  # PEP8: `lower_case_names`

def create_proteins():
    window_pr = ProteinsWindow()

def create_welcome():
    """Create welcome window."""
    
    # window
    global window_welcome
   
    window_welcome = tk.Tk()
    window_welcome.geometry("400x300")  # size of the window 
    window_welcome.title('Main')
    
    # button
    btn_proteins = tk.Button(window_welcome, text='Proteins', width=20, command=create_proteins)
    btn_proteins.grid(row=2, column=1)

    # keep the window open
    window_welcome.mainloop()  

# --- main ---

create_welcome()

PEP 8 -- Style Guide for Python Code

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