当用户按TKINTER中的新号码时，如何清除文本小部件内部的内容？

Question

text = ""

e = Text(window, width = 15, height = 2, font = ("Times New Roman", 24))
e.grid(column = 0, row = 0, columnspan=5)

def show_value(val): # Displays the text when user clicks buttons
    global text
    text+=str(val)
    e.insert(END, val)
    
def clear(): # Clears what's inside the text frame
    global text
    e.delete("1.0", "end")
    text = ""

def delete(): # Deletes the last value/character
    e.delete("end-2c") 

def equal(): # Computes
    global text
    try:
        text = str(eval(text))
        e.delete("1.0", "end")
        e.insert("1.0", text)
    except:
        clear()
        e.insert("1.0", "Error")

#Buttons

# button_negative = Button(window, text = "+/-", width = 6, font = ("Arial", 10)) # ADD THIS SOON
button_zero = Button(window, text = "0", width = 6, font = ("Arial", 10), bg = "black", fg = "white", command = lambda: show_value(0))
button_one = Button(window, text = "1", width = 6, font = ("Arial", 10), bg = "black", fg = "white", command = lambda: show_value(1))
button_two = Button(window, text = "2", width = 6, font = ("Arial", 10), bg = "black", fg = "white", command = lambda: show_value(2))
button_three = Button(window, text = "3", width = 6, font = ("Arial", 10), bg = "black", fg = "white", command = lambda: show_value(3))
button_four = Button(window, text = "4", width = 6, font = ("Arial", 10), bg = "black", fg = "white", command = lambda: show_value(4))
button_five = Button(window, text = "5", width = 6, font = ("Arial", 10), bg = "black", fg = "white", command = lambda: show_value(5))
button_six = Button(window, text = "6", width = 6, font = ("Arial", 10), bg = "black", fg = "white", command = lambda: show_value(6))
button_seven = Button(window, text = "7", width = 6, font = ("Arial", 10), bg = "black", fg = "white", command = lambda: show_value(7))
button_eight = Button(window, text = "8", width = 6, font = ("Arial", 10), bg = "black", fg = "white", command = lambda: show_value(8))
button_nine = Button(window, text = "9", width = 6, font = ("Arial", 10), bg = "black", fg = "white", command = lambda: show_value(9))
button_equals = Button(window, text = "=", width = 6, font = ("Arial", 10), bg = "#7C3D00", fg = "white", command = equal)
button_decimal = Button(window, text = ".", width = 6, font = ("Arial", 10), bg = "black", fg = "white", command = lambda: show_value("."))
button_add = Button(window, text = "+", width = 6, font = ("Arial", 10), bg = "black", fg = "white", command = lambda: show_value("+"))
button_subtract = Button(window, text = "-", width = 6, font = ("Arial", 10), bg = "black", fg = "white", command = lambda: show_value("-"))
button_divide = Button(window, text = "/", width = 6, font = ("Arial", 10), bg = "black", fg = "white", command = lambda: show_value("/"))
button_multiply = Button(window, text = "*", width = 6, font = ("Arial", 10), bg = "black", fg = "white", command = lambda: show_value("*"))
button_clear = Button(window, text = "AC", width = 6, font = ("Arial", 10), bg = "black", fg = "white", command = clear)
button_delete = Button(window, text = "DEL", width = 6, font = ("Arial", 10), bg = "black", fg = "white", command = delete)
button_left_bracket = Button(window, text = "(", width = 6, font = ("Arial", 10), bg = "black", fg = "white", command = lambda: show_value("("))
button_right_bracket = Button(window, text = ")", width = 6, font = ("Arial", 10), bg = "black", fg = "white", command = lambda: show_value(")"))

#button_negative.grid(row = 7, column = 0)
button_zero.grid(row = 7, column = 0)
button_decimal.grid(row = 7, column = 1)
button_equals.grid(row = 7, column = 3)
button_delete.grid(row = 7, column = 2)

button_one.grid(row = 5, column = 0)
button_two.grid(row = 5, column = 1)
button_three.grid(row = 5, column = 2)
button_add.grid(row = 5, column = 3)

button_four.grid(row = 4, column = 0)
button_five.grid(row = 4, column = 1)
button_six.grid(row = 4, column = 2)
button_subtract.grid(row = 4, column = 3)

button_seven.grid(row = 3, column = 0)
button_eight.grid(row = 3, column = 1)
button_nine.grid(row = 3, column = 2)
button_multiply.grid(row = 3, column = 3)

button_clear.grid(row = 2, column = 0)
button_left_bracket.grid(row = 2, column = 1)
button_right_bracket.grid(row = 2, column = 2)
button_divide.grid(row = 2, column = 3)

window.mainloop()

我仍在学习Python，并想创建一个计算器作为我的第一个项目。我的问题是，当用户要计算8 + 8并单击“等价”按钮时，它将显示16。但是，我希望将其清除，而无需按所有清除按钮时，当用户想要计算一些新事物时，EG 56 + 6而是显示。我该怎么做？

Answer 1

在像TKINTER一样操纵GUI时，建议您使用Python类，因为操纵元素会更容易。

至于您的问题，类似的东西是否适合您的需求？

#!/usr/bin/python3
import tkinter as tk

text = ""

CALCUL_DONE=False

window=tk.Tk()

e = tk.Text(window, width = 15, height = 2, font = ("Times New Roman", 24))
e.grid(column = 0, row = 0, columnspan=5)

def clear(): # Clears what's inside the text frame
    global text
    e.delete("1.0", "end")
    text = ""

def show_value(val): # Displays the text when user clicks buttons
    global text, CALCUL_DONE
    if CALCUL_DONE:
        clear()
        CALCUL_DONE=False
    text+=str(val)
    e.insert(tk.END, val)
    

def delete(): # Deletes the last value/character
    e.delete("end-2c") 

def equal(): # Computes
    global text, CALCUL_DONE
    try:
        text = str(eval(text))
        e.delete("1.0", "end")
        e.insert("1.0", text)
        CALCUL_DONE=True
    except:
        clear()
        e.insert("1.0", "Error")

#Buttons

# button_negative = tk.Button(window, text = "+/-", width = 6, font = ("Arial", 10)) # ADD THIS SOON
button_zero = tk.Button(window, text = "0", width = 6, font = ("Arial", 10), bg = "black", fg = "white", command = lambda: show_value(0))

[...]

button_right_bracket = tk.Button(window, text = ")", width = 6, font = ("Arial", 10), bg = "black", fg = "white", command = lambda: show_value(")"))

#button_negative.grid(row = 7, column = 0)
button_zero.grid(row = 7, column = 0)

[...]

button_divide.grid(row = 2, column = 3)

window.mainloop()

我添加了一个布尔值（calcul_done）在false上初始化的，因此当您单击“+”，“” - “，...它将其值更改为true，然后再次单击一个数字时，调用了funtion clear（）。

Answer 2

@sramazoth 答案是正确的基本想法使用键盘输入值（而不仅仅是显示的计算器的按钮）。问题是由于使用该全局文本正在使用。您的尝试使其内容与文本中的内容相同，仅用于单击显示的button s，但用户也可以直接输入通过键盘的文本窗口小部件的值，您的代码不会检测到。

我通过执行两件事（除了添加global flag之外，我都建议@sramazoth建议）：

1. 消除全局文本 string acter clibal，这真的没有必要由于您需要的文本已经存储在text小部件本身中。
2. 添加了一个按键事件处理程序，并将其绑定到text窗口小部件，该小部件将设置全局标志，就像单击一个按钮输入值一样。

您还需要了解，将eRAT（）应用于不受信任的用户输入是严重的安全危害，因为它们可以输入可以做坏事的任意代码。

鉴于此警告，这是修改的代码：

import tkinter as tk
from tkinter.constants import *

clear_flag = False  # Indicates when Text widget should be cleared.

window = tk.Tk()

e = tk.Text(window, width=15, height=2, font=("Times New Roman", 24))
e.grid(column=0, row=0, columnspan=5)


def on_keypress(event):
    global clear_flag
    if clear_flag:
        clear()
        clear_flag = False

e.bind('<KeyPress>', on_keypress)

def show_value(val): # Displays the expression when user clicks buttons
    global clear_flag
    if clear_flag:
        clear()
        clear_flag = False
    e.insert(END, val)

def clear(): # Clears what's inside the expression frame
    e.delete("1.0", "end")

def delete(): # Deletes the last value/character
    e.delete("end-2c")

def equal(): # Computes
    global clear_flag
    try:
        result = eval(e.get("1.0", END))
        e.delete("1.0", "end")
        e.insert("1.0", result)
    except Exception as exc:
        clear()
        e.insert("1.0", "Error")
    clear_flag = True

#Buttons

# button_negative = tk.Button(window, text="+/-", width=6, font=("Arial", 10)) # ADD THIS SOON
button_zero = tk.Button(window, text="0", width=6, font=("Arial", 10), bg="black", fg="white", command=lambda: show_value(0))
button_one = tk.Button(window, text="1", width=6, font=("Arial", 10), bg="black", fg="white", command=lambda: show_value(1))
button_two = tk.Button(window, text="2", width=6, font=("Arial", 10), bg="black", fg="white", command=lambda: show_value(2))
button_three = tk.Button(window, text="3", width=6, font=("Arial", 10), bg="black", fg="white", command=lambda: show_value(3))
button_four = tk.Button(window, text="4", width=6, font=("Arial", 10), bg="black", fg="white", command=lambda: show_value(4))
button_five = tk.Button(window, text="5", width=6, font=("Arial", 10), bg="black", fg="white", command=lambda: show_value(5))
button_six = tk.Button(window, text="6", width=6, font=("Arial", 10), bg="black", fg="white", command=lambda: show_value(6))
button_seven = tk.Button(window, text="7", width=6, font=("Arial", 10), bg="black", fg="white", command=lambda: show_value(7))
button_eight = tk.Button(window, text="8", width=6, font=("Arial", 10), bg="black", fg="white", command=lambda: show_value(8))
button_nine = tk.Button(window, text="9", width=6, font=("Arial", 10), bg="black", fg="white", command=lambda: show_value(9))
button_equals = tk.Button(window, text="=", width=6, font=("Arial", 10), bg="#7C3D00", fg="white", command=equal)
button_decimal = tk.Button(window, text=".", width=6, font=("Arial", 10), bg="black", fg="white", command=lambda: show_value("."))
button_add = tk.Button(window, text="+", width=6, font=("Arial", 10), bg="black", fg="white", command=lambda: show_value("+"))
button_subtract = tk.Button(window, text="-", width=6, font=("Arial", 10), bg="black", fg="white", command=lambda: show_value("-"))
button_divide = tk.Button(window, text="/", width=6, font=("Arial", 10), bg="black", fg="white", command=lambda: show_value("/"))
button_multiply = tk.Button(window, text="*", width=6, font=("Arial", 10), bg="black", fg="white", command=lambda: show_value("*"))

button_clear = tk.Button(window, text="AC", width=6, font=("Arial", 10), bg="black", fg="white", command=clear)
button_delete = tk.Button(window, text="DEL", width=6, font=("Arial", 10), bg="black", fg="white", command=delete)

button_left_bracket = tk.Button(window, text="(", width=6, font=("Arial", 10), bg="black", fg="white", command=lambda: show_value("("))
button_right_bracket=tk.Button(window, text=")", width=6, font=("Arial", 10), bg="black", fg="white", command=lambda: show_value(")"))

#button_negative.grid(row = 7, column = 0)
button_zero.grid(row = 7, column = 0)
button_decimal.grid(row = 7, column = 1)
button_equals.grid(row = 7, column = 3)
button_delete.grid(row = 7, column = 2)

button_one.grid(row = 5, column = 0)
button_two.grid(row = 5, column = 1)
button_three.grid(row = 5, column = 2)
button_add.grid(row = 5, column = 3)

button_four.grid(row = 4, column = 0)
button_five.grid(row = 4, column = 1)
button_six.grid(row = 4, column = 2)
button_subtract.grid(row = 4, column = 3)

button_seven.grid(row = 3, column = 0)
button_eight.grid(row = 3, column = 1)
button_nine.grid(row = 3, column = 2)
button_multiply.grid(row = 3, column = 3)

button_clear.grid(row = 2, column = 0)
button_left_bracket.grid(row = 2, column = 1)
button_right_bracket.grid(row = 2, column = 2)
button_divide.grid(row = 2, column = 3)

window.mainloop()