如何更新tkinter中的“live”文本框？

Question

I would like to ask how would I go about maybe creating a 'LIVE' text box in python? This program is a simulator for a vending machine (code below). I want there to be a text box showing a live credit update How do you do that in tkinter?

For Example: Say there is a box for credit with 0 inside it in the middle of the window. When the 10p button is pressed the box for credit should change from '0' to '0.10'. Is it possible to do thit in tkinter and python 3.3.2? Thank you in advance!

import sys
import tkinter as tk

credit = 0
choice = 0

credit1 = 0
coins = 0
prices = [200,150,160,50,90]
item = 0
i = 0
temp=0
n=0
choice1 = 0
choice2 = 0

credit1 = 0
coins = 0
prices = [200,150,160,50,90]
item = 0
i = 0
temp=0
n=0
choice1 = 0
choice2 = 0

def addTENp():
    global credit
    credit+=0.10

def addTWENTYp():
    global credit
    credit+=0.20

def addFIFTYp():
    global credit
    credit+=0.50

def addPOUND():
    global credit
    credit+=1.00

def insert():
    insert = Tk()

    insert.geometry("480x360")
    iLabel = Label(insert, text="Enter coins.[Press Buttons]").grid(row=1, column=1)

    tenbutton = Button(insert, text="10p", command = addTENp).grid(row=2, column=1)
    twentybutton = Button(insert, text="20p", command = addTWENTYp).grid(row=3, column=1)
    fiftybutton = Button(insert, text="50p", command = addFIFTYp).grid(row=4, column=1)
    poundbutton = Button(insert, text="£1", command = addPOUND).grid(row=5, column=1)


insert()

Answer 1

Sure you can! Just add another label to the frame, and update the text attribute whenever one of your add functions is called. Also, you can simplify that code, using one add function for all the different amounts.

def main():
    frame = Tk()
    frame.geometry("480x360")

    Label(frame, text="Enter coins.[Press Buttons]").grid(row=1, column=1)
    display = Label(frame, text="") # we need this Label as a variable!
    display.grid(row=2, column=1)

    def add(amount):
        global credit
        credit += amount
        display.configure(text="%.2f" % credit)

    Button(frame, text="10p", command=lambda: add(.1)).grid(row=3, column=1)
    Button(frame, text="20p", command=lambda: add(.2)).grid(row=4, column=1)
    Button(frame, text="50p", command=lambda: add(.5)).grid(row=5, column=1)
    Button(frame, text="P1",  command=lambda: add(1.)).grid(row=6, column=1)
    frame.mainloop()

main()

Some more points:

• note that you define many of your variables twice
• you should not give a variable the same name as a function, as this will shadow the function
• probably just a copy paste error, but you forgot to call mainloop and your tkinter import is inconsistent with the way you use the classes (without tk prefix)
• you can do the layout right after creating the GUI elements, but note that in this case not the GUI element will be bound to the variable, but the result of the layouting function, which is None

Answer 2

Borrowing a framework from tobias_k's excellent answer, I would recommend you use a DoubleVar instead.

from tkinter import ttk
import tkinter as tk

def main():
    frame = Tk()
    frame.geometry("480x360")

    credit = tk.DoubleVar(frame, value=0)
    # credit = tk.StringVar(frame, value="0")

    ttk.Label(frame, textvariable = credit).pack()

    def add_credit(amt):
        global credit
        credit.set(credit.get() + amt)
        # new_credit = str(int(credit.get().replace(".",""))+amt)
        # credit.set(new_credit[:-2]+"."+new_credit[-2:])

    ttk.Button(frame, text="10p", command = lambda: add_credit(0.1)).pack()
    # ttk.Button(frame, text="10p", command = lambda: add_credit(10)).pack()

    ttk.Button(frame, text="20p", command = lambda: add_credit(0.2)).pack()
    # ttk.Button(frame, text="20p", command = lambda: add_credit(20)).pack()

    ttk.Button(frame, text="50p", command = lambda: add_credit(0.5)).pack()
    # ttk.Button(frame, text="50p", command = lambda: add_credit(50)).pack()

    ttk.Button(frame, text="P1",  command = lambda: add_credit(1.0)).pack()
    # ttk.Button(frame, text="P1",  command = lambda: add_credit(100)).pack()

    frame.mainloop()

The comments in that code is an alternate implementation that will work better, if only just. This will guarantee you won't have any strange floating-point errors in your code.