Tkinter: one big class for the whole application

Hello StackOverflow Community,

I am the first GUI coder looking for advice. I'm doing my Master of Science in Physical Chemistry, for context.

I have a simple question: Is it considered bad practice to completely tie my code to a single class? I tried to split my code into classes, but I can't seem to get the magic initialization method when working with multiple classes. For reference, I've added my own init . Maybe you could help me understand how I could separate the whole thing into different classes that could go into separate modules.

Thank!

class ApplicationUI(tk.Tk):
    def __init__(self):
        """
        Initialises the GUI and parent.
        """
        tk.Tk.__init__(self)
        self.create_canvas()
        self.create_menus()
        self.create_main_buttons()

        self.data = {}
        self.call_counter = 0

        self.file_opts = {}
        self.file_opts['filetypes'] = [('Text Files', '.txt'),('CSV Files', '.csv'),('All Files', '.*')]
        self.file_opts['initialdir'] = 'C:\\Users\jcos\Documents'
        self.file_opts['title'] = 'File'

app = ApplicationUI()
app.mainloop()