title: _tkinter.TclError: invalid command name ".54870736.54870896.54871216.54871728"
body: <p>My program is a timed addition quiz. It works just fine but this error message keeps appearing after I input an incorrect answer (command=submit_answer). This is the whole error message:</p>
  
  <pre><code>Exception in Tkinter callback
  Traceback (most recent call last):
    File "C:\Users\Maggie\AppData\Local\Programs\Python\Python35-32\lib\tkinter\__init__.py", line 1549, in __call__
      return self.func(*args)
    File "C:\Users\Maggie\AppData\Local\Programs\Python\Python35-32\lib\tkinter\__init__.py", line 596, in callit
      func(*args)
    File "C:\Users\Maggie\Documents\python\prototype2.py", line 115, in countdown
      self.label.configure(text="%d" % self.remaining)
    File "C:\Users\Maggie\AppData\Local\Programs\Python\Python35-32\lib\tkinter\__init__.py", line 1330, in configure
      return self._configure('configure', cnf, kw)
    File "C:\Users\Maggie\AppData\Local\Programs\Python\Python35-32\lib\tkinter\__init__.py", line 1321, in _configure
      self.tk.call(_flatten((self._w, cmd)) + self._options(cnf))
  _tkinter.TclError: invalid command name ".54870736.54870896.54871216.54871728"
  </code></pre>
  
  <p>This is the code to my program:</p>
  
  <pre><code>class Add(tk.Frame):
  
      def __init__(self, parent, controller):
          tk.Frame.__init__(self, parent, background="blue")
          button = tk.Button(self, text="Main Menu", font=LARGE_FONT, background="white",
                             command=lambda: controller.show_frame(Main))
          button.place(relx=0.83, rely=0.92)
  
          self.button4 = tk.Button(self, text="Start Game", font=LARGE_FONT, background="white",
                             command=self.time_start)
          self.button4.place(relx=0.4, rely=0.8, relheight=0.1, relwidth=0.2)
  
          self.after_id = None
  
      def time_start(self):
          self.button4.destroy()
  
          self.x = int(random.uniform(1,10))
          self.y = int(random.uniform(50,100))
          self.z = int(random.uniform(10,50))
          print(self.x+self.y+self.z)
  
          self.qlabel = tk.Label(self, text= (self.x,"+",self.y,"+",self.z,"=",), font=WORD_FONT, bg="blue")
          self.qlabel.place(relx=0.25, rely=0.3, relheight=0.05, relwidth=0.3)
  
          self.e1 = tk.Entry(self)
          self.e1.place(relx=0.5, rely=0.3, relheight=0.05, relwidth=0.2)
  
          self.ebutton = tk.Button(self, text="Done", font=TITLE_FONT, background="white",
                              command=self.submit_answer)
          self.ebutton.place(relx=0.35, rely=0.5, relheight=0.2, relwidth=0.3)
  
          self.label = tk.Label(self, text="", width=10, font=LARGE_FONT, bg="white")
          self.label.place(relx=0.1, rely=0.1)
          self.remaining = 0
          self.countdown(10)
  
      def submit_answer(self):
          a = (self.x+self.y+self.z)
          if int(self.e1.get()) == a:
              answerlabel = tk.Label(self, text="Correct!", font=LARGE_FONT, background="blue")
              answerlabel.place(relx=0.42, rely=0.1, relheight=0.1, relwidth=0.2)
              self.label.destroy()
              self.qlabel.destroy()
              self.e1.destroy()
              self.ebutton.destroy()
              self.after_cancel(self.after_id)
              self.time_start()
          else:
              answerlabel = tk.Label(self, text="Game Over.", font=LARGE_FONT, background="blue")
              answerlabel.place(relx=0.42, rely=0.1, relheight=0.1, relwidth=0.2)
              self.ebutton.destroy()
              self.label.destroy()
              self.restartbutton = tk.Button(self, text="Reset Game", font=LARGE_FONT, background="white",
                                    command= self.reset_game)
              self.restartbutton.place(relx=0.65, rely=0.92)
  
      def countdown(self, remaining = None):
          if remaining is not None:
              self.remaining = remaining
          if self.remaining &lt;= 0:
              self.after_id = None
              self.label.configure(text="Time's up!")
              self.ebutton.destroy()           
          else:
              self.label.configure(text="%d" % self.remaining)
              self.remaining = self.remaining - 1
              self.after_id = self.after(1000, self.countdown)
  
      def reset_game(self):
          self.button4 = tk.Button(self, text="Start Game", font=LARGE_FONT, background="white",
                             command=self.time_start)
          self.button4.place(relx=0.4, rely=0.8, relheight=0.1, relwidth=0.2)
          self.label.destroy()
          self.qlabel.destroy()
          self.e1.destroy()
          self.ebutton.destroy()
          blanklabel = tk.Label(self, background="blue")
          blanklabel.place(relx=0.42, rely=0.1, relheight=0.1, relwidth=0.2)
          self.restartbutton.destroy()
  </code></pre>