title: Validate tkinter user input, presence check
body: <p>I need to validate user inputs on a tkinter GUI. I will need to have a presence check, a format check(a date) and one of the inputs can only be one of 3 options and I am not sure how to do these. I have looked at other examples but they are hard to understand because I have not been using classes. Does anybody know how to do this?</p>
  
  <p>Here is some example code</p>
  
  <pre><code>Entry1= Entry(window, bg="Blue", fg="white",font="40")
  Entry2= Entry(window, bg="Blue", fg="white",font="40")
  Entry3= Entry(winodw, bg="Blue", fg="white",font="40")
  
  
  #Assigning the input boxes to area on the screen
  Entry1.grid(row=1, column=1)
  Entry2.grid(row=2, column=1)
  Entry3.grid(row=3, column=1)
  
  forename=Entry1.get()
  surname=Entry2.get()
  dateofbirth=Entry3.get()
  </code></pre>