Updating text field on a tkinter canvas

Question

First time I have created a GUI using tkinter in Python. I have worked with wxPython and not had this same issue but I never used a canvas. The thought process behind the canvas is to eventually add animations. I have created a grid layout with one of the grids being a canvas. I am attempting to update a score field using itemconfig with no luck getting the two score fields to update on the canvas. My code is below. Any recommendations for how to update the two scores on a canvas? I want the old score to get removed before the new score is written to the screen. Thanks for taking a look. Forgive the globals, they are to be removed as this progresses.

class Gui(Frame):
def __init__(self, root):
    self.root=root
    self.initUI()

def initUI(self):
    global score1, score2   # these are ints
    score1str = str(score1)
    score2str = str(score2)

    root.title("Table Tennis Scoreboard")

    self.canvas = Canvas(root, width=640, height=480, background='green')
    self.canvas.grid(row=0,column=1)

    self.canvas.create_text(185, 90, anchor=W, font=('Calibri', 20),
                                             text="Let's play Table Tennis!")

    self.canvas.create_rectangle(75, 120, 275, 320, outline="red", fill="red")
    self.canvas.create_rectangle(370, 120, 565, 320, outline="blue", fill="blue")

    self.canvas.create_text(125, 130, anchor=W, font=('Calibri', 20),
                                             text="Player 1")
    self.canvas.create_text(425, 130, anchor=W, font=('Calibri', 20),
                                             text="Player 2")

    self.score1_id = self.canvas.create_text(135, 250, anchor=W, font=('Arial', 100),
                                             text=score1str)
    self.score2_id = self.canvas.create_text(435, 250, anchor=W, font=('Arial', 100),
                                             text=score2str)

    frame = Frame(self.root, relief=RAISED, borderwidth=2, background='white')
    frame.grid(row=0,column=0)

    p1up = Button(frame,text="Player1 +1", height=2, width=10, background='red', command=self.add('one'))
    p1up.grid(row = 0,column = 0, padx=10, pady=(20,5))
    p1down = Button(frame,text="Player1 -1", height=2, width=10, background='red', command=self.subtract('one'))
    p1down.grid(row = 1,column = 0, padx=10, pady=(5,100))
    p2up = Button(frame,text="Player2 +1", height=2, width=10, background='blue', command=self.add('two'))
    p2up.grid(row = 3,column = 0, padx=10, pady=5)
    p2down = Button(frame,text="Player2 -1", height=2, width=10, background='blue', command=self.subtract('two'))
    p2down.grid(row = 4,column = 0, padx=10, pady=(5,100))
    reset = Button(frame,text="Reset", height=2, width=10, command=self.new_game())
    reset.grid(row = 6,column = 0, padx=10, pady=(5,20))

def new_game(self):
    global score1, score2   # these are ints
    score1 = 0
    score2 = 0
    self.update_score()

def add(self, player):
    global score1, score2  # these are ints
    self.player = player
    if self.player == 'one':
        #if score1 < 11:
        score1 += 1
    elif self.player == 'two':
        #if score2 < 11:
        score2 += 1
    self.update_score()
    return

def subtract(self, player):
    global score1, score2  # these are ints
    self.player = player
    if self.player == 'one':
        if score1 > 0:
            score1 = score1 - 1
    elif self.player == 'two':
        if score2 > 0:
            score2 -= 1
    self.update_score()
    return

def update_score(self):
    global score1, score2   # these are ints

    score1str = str(score1)
    score2str = str(score2)

    self.canvas.itemconfig(self.score1_id, text=score1str)
    self.canvas.itemconfig(self.score2_id, text=score2str)

    return

if __name__== '__main__':
    root=Tk()
    gui=Gui(root)
    root.mainloop()

What does "no luck" mean? Are you getting an error? Does the program crash? Do the wrong words appear? — Bryan Oakley, Dec 18 '14 at 00:18
You delete the canvas item, i.e. text and then do a create_text statement with the new text. Take a look at the delete example at http://effbot.org/tkinterbook/canvas.htm — , Dec 18 '14 at 02:42
No luck in that the scores do not update. The program loads and the interface looks fine, albeit rudimentary. What I want to happen is I hit a button and the score updates. I tried to delete the fields off the canvas and recreate them but all that happens is the zero is displayed and no matter what button I press, the score never changes after it loads the first time. — Sherd, Dec 18 '14 at 02:57
Does this answer your question? [Why is my Button's command executed immediately when I create the Button, and not when I click it?](https://stackoverflow.com/questions/5767228/why-is-my-buttons-command-executed-immediately-when-i-create-the-button-and-no) — Karl Knechtel, Sep 05 '22 at 05:04

score 2 · Accepted Answer · edited May 23 '17 at 11:58

The problem is that you're not assigning functions to the buttons, but return values of function calls. For example:

  reset = Button(frame,text="Reset", height=2, width=10, command=self.new_game())

Assigns None to the command, because that's what self.new_game() returns. You should change this to:

  reset = Button(frame,text="Reset", height=2, width=10, command=self.new_game)

Which assigns the function self.new_game to the button's command, instead of None.

Then, for the other buttons, to pass an argument to the button's command you should use a lambda function like:

 p1up = Button(frame,text="Player1 +1", height=2, width=10, background='red', command=lambda: self.add('one'))

This assigns an anonymous function which calls self.add('one') to the button's commmand.

Also see: Why is Button parameter "command" executed when declared?

This question is a **clear** duplicate; it's inappropriate to answer and then give a "see also" link to the duplicate. — Karl Knechtel, Sep 05 '22 at 05:04

Updating text field on a tkinter canvas

1 Answers1