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How to swap between pages / windows in Tkinter

I have tried googling and everyone seems to have structured their code completely differently. I understand the base level tkinter, however I do not understand how people are using classes and def's to swap pages. How can I swap from my main window to my second one? (and not open the second one after the main is closed)
import tkinter as tk
main = tk.Tk()
main.title("Main Program")
firstlabel = tk.Label(main, text="This is a program!")
firstlabel.pack()
main.mainloop()
second = tk.Tk()
second.title("Second Program")
firstlabel = tk.Label(second, text="This is another program!")
firstlabel.pack()
second.mainloop()
EDIT: (solution)
import tkinter as tk
class Application(tk.Tk):
def __init__(self, *args, **kwargs):
tk.Tk.__init__(self, *args, **kwargs)
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):
frame = F(container, self)
self.frames[F] = frame
frame.grid(row=0, column=0, sticky="nsew")
self.show_frame(StartPage)
def show_frame(self, cont):
frame = self.frames[cont]
frame.tkraise()
class StartPage(tk.Frame):
def __init__(self, parent, controller):
tk.Frame.__init__(self,parent)
label = tk.Label(self, text="Start Page", font=("Consolas", 30))
label.pack(pady=10,padx=10)
button = tk.Button(self, text="Visit Page 1", command=lambda: controller.show_frame(PageOne))
button.pack()
class PageOne(tk.Frame):
def __init__(self, parent, controller):
tk.Frame.__init__(self, parent)
label = tk.Label(self, text="Page One!!!", font=("Consolas", 30))
label.pack(pady=10,padx=10)
button1 = tk.Button(self, text="Back to Home", command=lambda: controller.show_frame(StartPage))
button1.pack()
app = Application()
app.mainloop()

One way do this is by clearing everything (every widget), with this function:
def clear(app):
# Delete everything else in app
widget_list = app.winfo_children()
for item in widget_list:
if item.winfo_children():
widget_list.extend(item.winfo_children())
for item in widget_list:
item.pack_forget()
And then puting in the new window you want to swap to (every window should hav its own frame to make it simpler).

Try this::::
tk.Toplevel(main)

Automatically updating a tkinter label that isn't directly accessible

I want to create a simple GUI for a constant data that comes through Serial. I decided to use tkinter. The value reading is updated and should be shown in a label. I created separate classes for the container and the other pages. I defined the container as such:
class Gui(Tk):
def __init__(self, *args, **kwargs):
Tk.__init__(self, *args, **kwargs)
container = Frame(self)
container.pack(side="top", fill = "both", expand = TRUE)
container.grid_rowconfigure(0, weight = 1)
self.frames={}
for F in (StartPage, PageOne):
frame = F(container, self)
self.frames[F] = frame
frame.grid(row = 0, column = 0, sticky = "nsew")
frame.UpdateMe()
self.show_frame(StartPage)
def show_frame(self, cont):
frame = self.frames[cont]
frame.tkraise()
And the page showing the label:
class PageOne(Frame):
def __init__(self, parent, controller):
Frame.__init__(self,parent)
global reading
self.label1text = StringVar()
self.label1 = Label(self, textvariable = label1text)
self.label1.pack()
button1 = Button (self, text = "Show Start Page", command = lambda: controller.show_frame(StartPage))
button1.pack()
self.label1text.set(reading)
def UpdateMe(self):
global reading
self.lable1text.set(reading)
Now, to initialize the GUI:
root = Gui()
root.mainloop()
However, since mainloop() is blocking, any argument coming after that wouldn't be executed; I could get around that with update and update_idletasks. However, I still don't know how I could call the function UpdateMe() inside PageOne()when I only created an instantiation of the Gui(). Is there a way for me to solve this or remediate my understanding of classes and object programming?

Since you cannot create StringVar without initializing Tk() (for your case, it is Gui()), so you need to create the reading variable inside Gui() and PageOne.label1 uses it as its textvariable. Below is an example based on your code:
from tkinter import *
from random import randint
class Gui(Tk):
def __init__(self, *args, **kwargs):
Tk.__init__(self, *args, **kwargs)
container = Frame(self)
container.pack(side="top", fill="both", expand=True)
container.grid_rowconfigure(0, weight=1)
container.grid_columnconfigure(0, weight=1)
self.reading = StringVar() # create the StringVar for PageOne
self.frames = {}
for F in (StartPage, PageOne):
frame = F(container, self)
frame.grid(row=0, column=0, sticky="nsew")
self.frames[F] = frame
self.show_frame(StartPage)
def show_frame(self, cont):
self.frames[cont].tkraise()
class StartPage(Frame):
def __init__(self, parent, controller):
Frame.__init__(self, parent)
button1 = Button (self, text="Show Page 1", command=lambda: controller.show_frame(PageOne))
button1.pack(fill="both", expand=True)
class PageOne(Frame):
def __init__(self, parent, controller):
Frame.__init__(self, parent)
self.label1 = Label(self, textvariable=controller.reading) # refer to Gui.reading StringVar
self.label1.pack(fill='x')
button1 = Button (self, text="Show Start Page", command=lambda: controller.show_frame(StartPage))
button1.pack(fill='x')
# use .after() to simulate the update of reading variable periodically
def update_reading():
app.reading.set(randint(0, 10000))
print('reading:', app.reading.get())
app.after(1000, update_reading)
app = Gui()
update_reading() # start the simulation task of updating reading variable
app.mainloop()
Note that I have created a function update_reading() to simulate the update of reading variable periodically using after() function.

Function to switch between two frames in tkinter

I'm looking through the code at passing-functions-parameters-tkinter-using-lambda, and needed a tad more functionality inside his class PageOne(tk.Frame). Instead of using lambda commands below (as he did):
button1 = tk.Button(self, text="Back to Home",
command=lambda: controller.show_frame(StartPage))`
I'd like to be able to create a function that had an if/then hierarchy inside of it... specifically to check if all other inputs on PageOne had been fulfilled first (which I then know how to do) before allowing a frame change.
If this can be done individually using lambda, even better. Can anyone help me out?
Update: Using Bryan's advice and reformatting for the original code he linked, I now have:
class App(tk.Tk):
def __init__(self, *args, **kwargs):
tk.Tk.__init__(self, *args, **kwargs)
tk.Tk.wm_title(self, "APP") #window heading
self.title_font = tkfont.Font(family='Helvetica', size=12) #options: weight="bold",slant="italic"
container = tk.Frame(self) #container = stack of frames; one on top is visible
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):
page_name = F.__name__
frame = F(parent=container, controller=self)
self.frames[page_name] = frame #puts all pages in stacked order
frame.grid(row=0, column=0, sticky="nsew")
self.show_frame("StartPage")
def show_frame(self, page_name): #show a frame for the given page name
frame = self.frames[page_name]
frame.tkraise()
class StartPage(tk.Frame):
def __init__(self, parent, controller):
tk.Frame.__init__(self, parent)
self.controller = controller
label = tk.Label(self, text="This is the start page", font=controller.title_font)
label.pack(side="top", fill="x", pady=10)
button1 = tk.Button(self, text="Go to Page One",
command=lambda: controller.show_frame("PageOne"))
button1.pack()
button2.pack()
class PageOne(tk.Frame):
def __init__(self, parent, controller):
tk.Frame.__init__(self, parent)
self.controller = controller
####FIX PART 1####
self.next1 = tk.Button(self,text="Next",padx=18,highlightbackground="black",
command=lambda: self.maybe_switch("PageTwo"))
self.next1.grid(row=10,column=1,sticky='E')
####FIX PART 2####
def maybe_switch(self, page_name):
if ###SOMETHING###:
self.controller.show_frame(page_name)
if __name__ == "__main__":
app = App()
app.mainloop()

You shouldn't put any logic in a lambda. Just create a normal function that has any logic you want, and call it from the button. It's really no more complicated that that.
class SomePage(...):
def __init__(...):
...
button1 = tk.Button(self, text="Back to Home",
command=lambda: self.maybe_switch_page(StartPage))
...
def maybe_switch_page(self, destination_page):
if ...:
self.controller.show_frame(destination_page)
else:
...
If you want a more general purpose solution, move the logic to show_frame, and have it call a method on the current page to verify that it is OK to switch.
For example:
class Controller(...):
...
def show_frame(self, destination):
if self.current_page is None or self.current_page.ok_to_switch():
# switch the page
else:
# don't switch the page
Then, it's just a matter of implementing ok_to_switch in every page class.

Tkinter Application showing blank screen while running

When I try to execute my Tkinter application created in python, it is giving me a blank application window. No Buttons/Labels are displaying. What may be the Issue ?
Codes are as follows:
import tkinter as tk
from tkinter import ttk
LARGE_FONT=("Verdana", 18)
class VNMSapp(tk.Tk):
def __int__(self, *args, **kwargs):
tk.Tk.__init__(self, *args, **kwargs)
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, AdminPage):
frame = F(container, self)
self.frames[F] = frame
frame.grid(row=0, column=0, sticky="nsew")
self.show_frame(StartPage)
def show_frame(self, cont):
frame = self.frames[cont]
frame.tkraise()
class StartPage(tk.Frame):
def __init__(self, parent, controller):
tk.Frame.__init__(self, parent)
label = tk.Label(text="THIS IS HOME PAGE", font=LARGE_FONT)
label.pack()
btn1 = tk.Button(self, text="Enter ADMIN PAGE",
command=lambda: controller.show_frame(AdminPage))
btn1.pack()
class AdminPage(tk.Frame):
def __init__(self, parent, controller):
tk.Frame.__init__(self, parent)
label = tk.Label(text="THIS IS ADMIN PAGE", font=LARGE_FONT)
label.pack()
btn1 = tk.Button(self, text="Enter HOME PAGE",
command=lambda: controller.show_frame(StartPage))
btn1.pack()
app = VNMSapp()
app.mainloop()
It is not giving me any error also.

There is a typo in the definition of the __init__() method for class VNMSapp:
def __int__(self, *args, **kwargs):
should be
def __init__(self, *args, **kwargs):
As a result your __init__() method is not being called, so your widgets are not created.
Once you correct that you will find an additional problem where you are using a list, but I think that you meant to use a dictionary:
self.frames= []
...
self.frames[F] = frame
the second line will fail raising a TypeError exception because list indices must be integers, which frame objects are not.
Fix that by initialising self.frames to an empty dict:
self.frames= {}

Switching Frames In PyQt4

I would like to know how I would go about doing the following in PyQt4:
import tkinter as tk
LARGE_FONT= ("Verdana", 12)
class SeaofBTCapp(tk.Tk):
def __init__(self, *args, **kwargs):
tk.Tk.__init__(self, *args, **kwargs)
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):
frame = F(container, self)
self.frames[F] = frame
frame.grid(row=0, column=0, sticky="nsew")
self.show_frame(StartPage)
def show_frame(self, cont):
frame = self.frames[cont]
frame.tkraise()
class StartPage(tk.Frame):
def __init__(self, parent, controller):
tk.Frame.__init__(self,parent)
label = tk.Label(self, text="Home", font=LARGE_FONT)
label.pack(pady=10,padx=10)
btn = tk.Button(self, text="Page One", command= lambda: controller.show_frame(PageOne))
btn.pack()
class PageOne(tk.Frame):
def __init__(self, parent, controller):
tk.Frame.__init__(self,parent)
label = tk.Label(self, text="Page One", font=LARGE_FONT)
label.pack(pady=10,padx=10)
btn = tk.Button(self, text="Home", command= lambda: controller.show_frame(StartPage))
btn.pack()
app = SeaofBTCapp()
app.mainloop()
I am going to have multiple pages and would like to have it easily defined. I am still very new to python coding and I'm still learning how PyQt4 works but my project will have atleast 4 pages that I need to switch between and I don't want the code to be too long by defining the same thing on every page's class. All help will be appreciated. Thank you in advance.

Take a look at QStackedWidget.
From the docs:
The QStackedWidget class provides a stack of widgets where only one widget is visible at a time.
Depending on what you are doing exactly, QWizard may be suited even better.
Both also exist for Qt4, but you should use Qt5 if you can.