Making python/tkinter label widget update?

Question

I'm working on getting a python/tkinter label widget to update its contents. Per an earlier thread today, I followed instructions on how to put together the widgets. At runtime, however, the label widget does NOT change contents, but simply retains its original content. As far as I can tell, decrement_widget() is never called at all. Any ideas?

def snooze (secs):
  """
  Snoozes for the given number of seconds. During the snooze, a progress
  dialog is launched notifying the 
  """

  root = Tkinter.Tk()
  prompt = 'hello'
  label1 = Tkinter.Label(root, text=prompt, width=len(prompt))
  label1.pack()

  remaining = secs

  def decrement_label ():
    text = "Snoozing %d sec(s)" % remaining
    remaining -= 1
    label1.config(text=text, width=100)
    label1.update_idletasks()

  for i in range(1, secs + 1):
    root.after(i * 1000, decrement_label )

  root.after((i+1) * 1000, lambda : root.destroy())
  root.mainloop()

Thanks!

--Steve

Answer 1

You'll want to set the label's textvariable with a StringVar; when the StringVar changes (by you calling myStringVar.Set("text here")), then the label's text also gets updated. And yes, I agree, this is a strange way to do things.

See the Tkinter Book for a little more information on this:

You can associate a Tkinter variable with a label. When the contents of the variable changes, the label is automatically updated:

v = StringVar()
Label(master, textvariable=v).pack()

v.set("New Text!")

Answer 2

I think you're getting a "referenced before assignment" error because Python thinks remaining is in the local scope.

In Python 3, you can say nonlocal remaining. But in Python 2, I don't believe there's a way to refer to a non-local, non-global scope. This worked for me:

remaining = 0

def snooze (secs):
  """
  Snoozes for the given number of seconds. During the snooze, a progress
  dialog is launched notifying the 
  """

  global remaining
  root = Tkinter.Tk()
  prompt = 'hello'
  label1 = Tkinter.Label(root, text=prompt, width=len(prompt))
  label1.pack()

  remaining = secs

  def decrement_label ():
    global remaining
    text = "Snoozing %d sec(s)" % remaining
    remaining -= 1
    label1.config(text=text, width=100)
    label1.update_idletasks()

  for i in range(1, secs + 1):
    root.after(i * 1000, decrement_label )

  root.after((i+1) * 1000, lambda : root.destroy())
  root.mainloop()