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 headingself.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 visiblecontainer.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 orderframe.grid(row=0, column=0, sticky="nsew")self.show_frame("StartPage")def show_frame(self, page_name): #show a frame for the given page nameframe = self.frames[page_name]frame.tkraise()class StartPage(tk.Frame):def __init__(self, parent, controller):tk.Frame.__init__(self, parent)self.controller = controllerlabel = 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 pageelse:# don't switch the page

Then, it's just a matter of implementing ok_to_switch in every page class.