switching windows in tkinter with classes

Question

in a [former question][1] received a perfect script from @acw1668 for creating popup-windows (see below).

How can this be rewritten in a form that the new windows are not popups but just a switch from one page to the next (the listboxes/candvas are not necessarily needed here)?

Edit: tried to amend the code according to @Bryan Oakley's suggestions. My issue here: I do not manage to pass the list lst from the GUI class to the other page classes without an error message:

 File "/.spyder-py3/temp.py", line 25, in __init__
    frame = F(parent=container, controller=self)

TypeError: __init__() missing 1 required positional argument: 'lst'

What am I missing here? And I do not understand what's happening here:

for F in (StartPage, PageOne, PageTwo):
                page_name = F.__name__
                frame = F(parent=container, controller=self,)

                self.frames[page_name] = frame

If somebody could explain, please?

import tkinter as tk
from tkinter import ttk


class GUI(tk.Tk):

    def __init__(self):

        tk.Tk.__init__(self)
        self.lst = ['a', 'b', 'c']
        container = tk.Frame(self)
        container.pack(side="top", fill="both", expand=True)
        container.grid_rowconfigure(0, weight=1)
        container.grid_columnconfigure(0, weight=1)

        self.frames = {}
        for F in (StartPage, PageOne, PageTwo):
            page_name = F.__name__
            frame = F(parent=container, controller=self,)

            self.frames[page_name] = frame

            # put all of the pages in the same location;
            # the one on the top of the stacking order
            # will be the one that is visible.
            frame.grid(row=0, column=0, sticky="nsew")

        self.show_frame("StartPage", self.lst)

    def show_frame(self, page_name):
        '''Show a frame for the given page name'''
        frame = self.frames[page_name]
        frame.tkraise()


    def show_popup(self, page, lst):

        win = page(self, lst)
        win.grab_set()          # make window modal
        self.wait_window(win)   # make window modal




class StartPage(tk.Frame):

    def __init__(self, parent, controller, lst):
        tk.Frame.__init__(self, parent)
        self.controller = controller
        self.lst = lst
         # ------------------------------------------------------------------- #
        label = tk.Label(self, text="Check this out")                         
        label.pack(pady=10,padx=10)

         # ------------------- create buttons ---------------------------------
        button1 = ttk.Button(self, text="show all",
                             width = 25, command=lambda: 
                                 controller.show_popup(App, self.lst))
        button1.pack(pady=10, padx=10)        
        button2 = ttk.Button(self, text="show page one",
                             width = 25, command=lambda: 
                                 controller.show_frame(PageOne))
        button2.pack(pady=10, padx=10)        


class PageOne(tk.Frame):

    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        self.controller = controller
        label = tk.Label(self, text="This is page 1")
        label.pack(side="top", fill="x", pady=10)
        button = tk.Button(self, text="Go to the start page",
                           command=lambda: controller.show_frame("StartPage"))
        button.pack()


class PageTwo(tk.Frame):

    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        self.controller = controller
        label = tk.Label(self, text="This is page 2")
        label.pack(side="top", fill="x", pady=10)
        button = tk.Button(self, text="Go to the start page",
                           command=lambda: controller.show_frame("StartPage"))
        button.pack()

class App(tk.Toplevel):

    def __init__(self, parent, lst):
        tk.Toplevel.__init__(self, parent)
        self.lst = lst
        self.title('This is the pop up window')
        self.geometry('400x200') 
        label = tk.Label(self, text=self.lst) 
        label.pack(side="top", fill="x", pady=10)
        parent.grid_rowconfigure(0, weight = 1)
        parent.grid_columnconfigure(0, weight = 1)

if __name__ == '__main__': 
    app = GUI() 
    app.mainloop()                  

  [1]: http://stackoverflow.com/questions/41181809/how-to-open-and-close-another-window-with-scrollbar-in-tkinter-for-python-3-5/41182843?noredirect=1#comment69580999_41182843

Answer 1

Your class initializers are defined like this:

class StartPage(tk.Frame):
    def __init__(self, parent, controller, lst):

In order to create an instance of this class it requires three arguments (plus self): parent, controller, and lst.

Now, let's look at how you're creating the instance:

frame = F(parent=container, controller=self,)

Notice how you have the parent and you have the controller, but you haven't passed in anything for lst. That is why the error states "missing 1 required positional argument: 'lst'" -- because you are literally missing one required argument named "lst".

To fix this problem, you simply need to provide this extra argument. For example:

frame = F(parent=container, controller=self, lst=self.lst)

HOWEVER, you probably shouldn't do that. The architecture of this little block of code you copied makes it possible to access values on the GUI class from any of the "page" classes without having to do any extra work.

Because this variable is an attribute of the GUI class, and you are passing a reference to the instance of the GUI class to each "page" (the controller attribute), you can access this data any time you want without having to pass it in at construction time. You can remove it from __init__ and from where you're creating the pages (ie: go back to the original code before your modifications), and then just use self.controller.lst whenever you need the value.

For example:

class SomePage(tk.Frame):
    def __init__(self, parent, controller):
        self.controller = controller
        ...
    def some_function(self):
        print("The value of 'lst' is:", self.controller.lst)