31

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()

5 Answers 5

49

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!")
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5 Comments

Per your recommendation, I changed the decrement_label function to 'text=...; remaining -=1; sv = Tkinter.StringVar(); sv.Set(text); label1.conf(text=sv, width=100); label1.update_idletasks()'. However, this has not had any effect on runtime behavior. The decrement_label function does NOT appear to be called at all!
I also figured out that the 'remaining -= 1' statement appears to be causing the problem. Python silently fails somehow when it encounters that statement. Is there something wrong with it?
You have to set the StringVar when you create the Label, and then modify that same instance of the StringVar. You shouldn't need to repeatedly call label1.conf. Post your fully updated code.
Note: using StringVar isn't strictly required. You can simply update the label widget directly with configure: l=Label(...); ...; l.configure(text="new text") which has the benefit of one less object to manage.
effbot.org is taking a break. Does anyone know where a mirror of the Tkinter book might be hosted?
9

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()

Comments

1
    import tkinter
    from tkinter import *

    # just init some vars
    remaining = 0                
    secs = 0
    root = tkinter.Tk()
    prompt = StringVar()

    def snooze (secs):
      """
      Snoozes for the given number of seconds. During the snooze, a progress
      dialog is launched notifying the 
      """
      def decrement_label ():
        global remaining, prompt
        remaining -= 1
        prompt.set('Snoozing %d sec(s)' % remaining)
        label1.update_idletasks()
        if not remaining:
          print("end ... ")
          root.destroy()

      global remaining
      prompt.set("hello")
      label1 = tkinter.Label(root, textvariable=prompt, width=30)
      label1.pack()

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

    snooze(10)
    root.mainloop()

Comments

1

To update text in a label you can try the following:

from tkinter import *

root = Tk()
root.title("Title")
root.geometry('300x300')


def clear_text(self):
    txtE.delete(0, 'end')


def new_label(event=None):
    Entree = txtE.get()
    lbl1['text'] = Entree.title()
    clear_text(txtE)


lbl1 = Label(root, text='Hello There')
lbl1.pack()
txtE = Entry(root)
txtE.focus()
txtE.pack()

Button(root, text='Enter', command=new_label).pack()
Button(root, text='Quit', command=root.destroy).pack(side=BOTTOM)
root.bind('<Return>', new_label)
root.mainloop()

Comments

0

I think you have to call snooze(secs) function

After that if your code again not works try this

Set a variable

Variable = StringVar()

In the label widget you can set "textvariable" argument to the above mentioned "Variable".

Eg: label1 = Label(root,textvariable = Variable).pack()

And you can update by setting a new value to "Variable"

Eg:Variable.set("hi")

Hope you got it !!!

Comments

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