python death date

from tkinter import *
import tkinter as tk
import time
import random
import sys
import os

def menu():

    wTitle = "Death Date - KyrosDesign"

    windowMain = tk.Tk()
    windowMain.geometry("400x200")
    windowMain.title(wTitle)
    windowMain.resizable(False, False)

    global dayBirth
    global monthBirth
    global yearBirth

    dayBirth = IntVar()
    monthBirth = IntVar()
    yearBirth = IntVar()

    global dayEntry
    global monthEntry
    global yearEntry

    Label(windowMain, text="Welcome in Death Date", font=("Sans-Serif",12), bg="#191919", fg="#ddd",width="50",height="2").pack()
    dayLabel = Label(windowMain, text="Day: ", font=("Sans-Serif",12), fg="#191919").place(y=58,x=65)
    dayEntry = Entry(windowMain, textvariable=dayBirth, fg="#191919",width="5",font=("Sans-Serif", 13))
    dayEntry.place(y=58,x=120)
    monthLabel = Label(windowMain, text="Month: ", font=("Sans-Serif",12), fg="#191919").place(y=98,x=65)
    monthEntry = Entry(windowMain, textvariable=monthBirth, fg="#191919",width="5",font=("Sans-Serif", 13))
    monthEntry.place(y=98,x=120)
    yearLabel = Label(windowMain, text="Year: ", font=("Sans-Serif",12), fg="#191919").place(y=138,x=65)
    yearEntry = Entry(windowMain, text="Day: ", textvariable=yearBirth, fg="#191919",width="5",font=("Sans-Serif", 13))
    yearEntry.place(y=138,x=120)
    Button(windowMain, text="Get Death Date", font=("Sans-Serif",9), bg="#191919", fg="#ddd",width="13",height="6", command = process).place(y=58,x=220)

    if __name__ == '__main__':
        windowMain.mainloop()

def process():

    if int(dayBirth) == 0:
        windowError = tk.Tk()
        windowError.geometry("400x200")
        windowError.title(wTitle)
        windowError.resizable(False, False)

        Label(windowError, text="Invalid Date", font=("Sans-Serif",12), bg="#191919", fg="#ddd",width="50",height="10").pack()
    else:
        dayB = dayEntry.get()
        monthB = monthEntry.get()
        yearB = yearEntry.get()

        wTitle = "Death Date - KyrosDesign"

        windowGame = tk.Tk()
        windowGame.geometry("400x200")
        windowGame.title(wTitle)
        windowGame.resizable(False, False)

        months = ['January','February','March','April','May','June','July','August','September','October','November ','December']
        days = random.randint(1,31)
        months = random.choice(months)
        years = random.randint(2019, 2119)
        age = years - int(yearB)
        result = '\nYou will die on {} {}, {}. At age {}.\n'.format(days, months, years, age)

        Label(windowGame, text="Result", font=("Sans-Serif",12), bg="#191919", fg="#ddd",width="50",height="2").pack()
        Label(windowGame, text=result, font=("Sans-Serif",12), bg="#191919", fg="#ddd",width="50",height="10").pack()


menu()