title: Python Tkinter changing label text
body: <p>I know that there are a lot of questions dealing with tkinter but I have looked at a bunch of them and none of them seem to help me.</p>
  
  <pre><code>import tkinter
  
  class Calculator:
  
    def __init__(self):
      window = tkinter.Tk()
      window.geometry("200x300")
      window.title("Calculator")
  
      lbl = tkinter.Label(window, text="placeholder", bg="blue", textvariable="labelText")
      lbl.grid(row=0, column=0, columnspan=3)
  
      self.firstNumArray = []
      self.secondNumArray = []
      self.operation = ""
      self.currentNum = "first"
  
      def appendNumber(self, number):
        print("Appending Number")
        if self.currentNum == "first":
          self.firstNumArray.append(number)
          print("".join(str(x) for x in self.firstNumArray))
          lbl.config(text="".join(str(x) for x in self.firstNumArray))
          window.update()
        else:
          self.secondNumArray.append(number)
  
      for i in range(1,4):
        string = "Creating button at ({0},{1})".format(0,i)
        print(string)
        button = tkinter.Button(text=i, command=lambda: appendNumber(self, i))
        button.grid(row=1, column=i-1)
  
      for i in range(1,4):
        string = "Creating button at ({0},{1})".format(1,i)
        print(string)
        button = tkinter.Button(text=i+3, command=lambda: appendNumber(self, i+3))
        button.grid(row=2, column=i-1)
  
      for i in range(1,4):
        string = "Creating button at ({0},{1})".format(2,i)
        print(string)
        button = tkinter.Button(text=i+6, command=lambda: appendNumber(self, i+6))
        button.grid(row=3, column=i-1)
  
  
      div = tkinter.Button(text="/")
      mult = tkinter.Button(text="*")
      add = tkinter.Button(text="+")
      sub = tkinter.Button(text="-")
  
      add.grid(row=1, column=3)
      sub.grid(row=2, column=3)
      mult.grid(row=3, column=3)
      div.grid(row=4, column=3)
  
      button = tkinter.Button(text="0")
      button.grid(row=4, column=1)
  
      window.mainloop()
  
  
  
  calc = Calculator()
  </code></pre>
  
  <p>When I launch the program the window opens. When I click on a button the text in the label does not change. I have tried using a <code>StringVar</code> as the <code>textvariable</code> and then calling the <code>set()</code> function, but that did not work either. I think it has to do with the scope of the function. I had to place the <code>appendNumber()</code> function inside the <code>__init__()</code> because for some reason <code>self.lbl = tkinter.Label()</code> makes nothing pop up at all.</p>