title: Pause for an event in python tkinter
body: <p>I am using a python 2.7 tkinter gui on a raspberry pi to automate some material testing. For the testing, multiple samples must be tested and it takes time to swap out the samples. I want to prompt text saying something like "Please insert sample one then press enter on keyboard" and have the function pause until enter has been pressed. Instead of pressing enter I could also use a tkinter button. Any ideas without using external libraries? I have tried a while loop in which I try and exit the loop once a button is pressed, but since the loop is running the button does not register.</p>
  
  <p>Sample code (removed lots of code and left what is relevant):</p>
  
  <pre><code>class App:
  def __init__(self,master):
  
      #self.WILTRON = Wiltron_54128A_GPIB()
  
      self.var = tk.StringVar()
      self.var.trace("w",self.getTest)
  
      self.okbutton = tk.IntVar()
      self.okbutton.trace("w",self.OKbutton)
  
      frame = Frame(master)
      frame.pack()
  
      #Initial GUI values
      self.var.set('Choose Test')
      testChoices = ['TEST']
      App.testOption = tk.OptionMenu(frame, self.var, *testChoices)
      App.testOption.grid(row=0, column=0)
      okButton = tk.Button(frame, text="     OK    ", command=self.OKbutton).grid(row=2, column=1)
  
  #Test routine functions
  def getTest(self, *args):
      test = self.var.get()
      sf = "IC Network Analyzer"
      root.title(sf)
  
      #####
      if test == "TEST":
          sample1 = self.WILTRON.Sample_Data()
          print 'Change out sample then press OK'
          #This is where I need to pause until the next sample has been inserted
          sample2 = self.WILTRON.Sample_Data()
          #ect.
      #####
  
  def OKbutton(self):
      #Whatever I need to do to make the button exit the pause
  </code></pre>