Creating a variable to store entry box information for other frames using tkinter

Question

This is my first time posting a question so I'm sorry in advanced if I do anything wrong when posting the question.

I am using tkinter and using the same code as an answer that was posted here that used classes to create and show frames:
Switch between two frames in tkinter

I want to be able to create global variables so that other frames can use them when needed. I tried using root = tk.Tk() and creating the global variable that way, but noticed that when doing that, not only did I not get the entry from the entry box, but it created a new window. I also tried global_var = tk.StringVar(), not having root = tk.Tk(), but got an error stating:

Traceback (most recent call last): File "app.py", line 6, in name_var = tk.StringVar() File "/usr/lib/python3.7/tkinter/init.py", line 480, in init Variable.init(self, master, value, name) File "/usr/lib/python3.7/tkinter/init.py", line 317, in init self._root = master._root() AttributeError: 'NoneType' object has no attribute '_root'

Is there a way for me to store that input from the entry box, and use it in another frame?

Source Code

class SampleApp(tk.Tk):
    def __init__(self, *args, **kwargs):
        tk.Tk.__init__(self, *args, **kwargs)
        self.title_font = tkfont.Font(family = 'Garamond', size = 18, weight = "bold", slant = "italic")

    #container we'll stack frames on top of each other, then the one we want to
        #visible will be raised above the others
        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, UserInfo):
            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")

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

class StartPage(tk.Frame):
    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        self.controller = controller
        self.controller.geometry("800x400")

        label = tk.Label(self, text = "Facial Recognition Lock", font = controller.title_font)
        label.pack(side = "top")

        button1 = tk.Button(self, text = "Go to Page One",
                        command = lambda: controller.show_frame("PageOne"))

        button2 = tk.Button(self, text = "Go to Page Two", command = lambda: controller.show_frame("PageTwo"))

        Exitbutton = tk.Button(self, text="Exit", width = 8, height = 3, command = self.Exit)

        button1.place(x = 200, y = 200)
        button2.place(x = 600, y = 200)
        Exitbutton.place(x = 350, y = 330)

    def Exit(self):
        self.controller.destroy()   

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 One", font = controller.title_font)
        label.pack(side = "top")

        button1 = tk.Button(self, text = "Go to Start Page",
                        command = lambda: controller.show_frame("StartPage"))

        button2 = tk.Button(self, text = "Go to Page Two",
                        command = lambda: controller.show_frame("PageTwo"))

        button3 = tk.Button(self, text = "User Info",
                        command = lambda: controller.show_frame("UserInfo"))

        button1.place(x = 200, y = 200)
        button2.place(x=400, y = 200)
        button3.place(x=300, y =340)     

class UserInfo(tk.Frame):    
    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        self.controller = controller
        label1 = tk.Label(self, text = "User Info", font = controller.title_font)  
        label1.pack(side = "top")

        label2 = tk.Label(self, text = "User's Name", font = "Arial 13")
        label2.place(x=100, y=100)

        button1 = tk.Button(self, text = "Go to Start Page",
                        command = lambda: controller.show_frame("StartPage"))

        button1.place(x=300, y = 350)

        nameEntry = tk.Entry(self, textvariable = name_var, bd = 5, font=('calibre',10,'normal'))
        nameEntry.place(x=220, y=100)

        showButton = tk.Button(self, text="Show", command = submit)

        showButton.place(x=200, y = 250)

if __name__ == "__main__":
    app = SampleApp()
    app.mainloop()  

Excluded PageTwo Class as it's similar to PageOne