Ttk tkinter python3 multiple frames / windows

The following application I created is used to showcase multiple windows in tkinter. The main problem is that none of the Entry controls, either in the bmi calculator or in the converter, takes values ​​in the input fields - they get a ValueError when I do the calculation.

from tkinter import *
from tkinter import ttk
from tkinter import messagebox

class App1 (ttk.Frame):
    def createWidgets (self):
        #text variables
        self.i_height = StringVar ()
        self.i_weight = StringVar ()
        self.o_bmi = StringVar ()

        #labels
        self.label1 = ttk.Label (self, text = "Enter your weight:"). grid (row = 0, column = 0, sticky = W)
        self.label2 = ttk.Label (self, text = "Enter your height:"). grid (row = 1, column = 0, sticky = W)
        self.label3 = ttk.Label (self, text = "Your BMI is:"). grid (row = 2, column = 0, sticky = W)

        #text boxes
        self.textbox1 = ttk.Entry (self, textvariable = self.i_weight) .grid (row = 0, column = 1, sticky = E)
        self.textbox2 = ttk.Entry (self, textvariable = self.i_height) .grid (row = 1, column = 1, sticky = E)
        self.textbox3 = ttk.Entry (self, textvariable = self.o_bmi) .grid (row = 2, column = 1, sticky = E)

        #buttons
        self.button1 = ttk.Button (self, text = "Cancel / Quit", command = self.quit) .grid (row = 3, column = 1, sticky = E)
        self.button1 = ttk.Button (self, text = "Ok", command = self.calculateBmi) .grid (row = 3, column = 2, sticky = E)

    def calculateBmi (self):
        try:
            self.weight = float (self.i_weight.get ())
            self.height = float (self.i_height.get ())
            self.bmi = self.weight / self.height ** 2.0
            self.o_bmi.set (self.bmi)
        except ValueError:
            messagebox.showinfo ("Error", "You can only use numbers.")
        finally:
            self.i_weight.set ("")
            self.i_height.set ("")

    def __init __ (self, master = None):
        ttk.Frame .__ init __ (self, master)
        self.grid ()
        self.createWidgets ()

class App2 (ttk.Frame):
    def create_widgets (self):
        "" "Create the widgets for the GUI" ""
        # 1 textbox (stringvar)
        self.entry = StringVar ()
        self.textBox1 = ttk.Entry (self, textvariable = self.entry) .grid (row = 0, column = 1)

        # 5 labels (3 static, 1 stringvar)
        self.displayLabel1 = ttk.Label (self, text = "feet"). grid (row = 0, column = 2, sticky = W)
        self.displayLabel2 = ttk.Label (self, text = "is equivalent to:"). grid (row = 1, column = 0)
        self.result = StringVar ()
        self.displayLabel3 = ttk.Label (self, textvariable = self.result) .grid (row = 1, column = 1)
        self.displayLabel4 = ttk.Label (self, text = "meters"). grid (row = 1, column = 2, sticky = W)

        # 2 buttons
        self.quitButton = ttk.Button (self, text = "Quit", command = self.quit) .grid (row = 2, column = 1, sticky = (S, E))
        self.calculateButton = ttk.Button (self, text = "Calculate", command = self.convert_feet_to_meters) .grid (row = 2, column = 2, sticky = (S, E))

    def convert_feet_to_meters (self):
        "" "Converts feet to meters, uses string vars and converts them to floats" ""
        self.measurement = float (self.entry.get ())
        self.meters = self.measurement * 0.3048
        self.result.set (self.meters)

    def __init __ (self, master = None):
        ttk.Frame .__ init __ (self, master)
        self.grid ()
        self.create_widgets ()

def button1_click ():
    root = Tk ()
    app = App1 (master = root)
    app.mainloop ()

def button2_click ():
    root = Tk ()
    app = App2 (master = root)
    app.mainloop ()

def main ():
    window = Tk ()
    button1 = ttk.Button (window, text = "bmi calc", command = button1_click) .grid (row = 0, column = 1)
    button2 = ttk.Button (window, text = "feet conv", command = button2_click) .grid (row = 1, column = 1)
    window.mainloop ()

if __name__ == '__main__':
    main ()

, python3? . . BTW - , # form1.Show()?