Tkinter计算器错误

Question

我正在制作一个简单的Python-Tk计算器，但是有一个错误：除非我在输入数字之前按下其中一个按钮，否则计算器将无法工作。当我这样做时，它会显示一个错误，提示“输入数值！”之后，它将计算输入的数字，但如果我只是打开它和输入数字，它不会工作

这是我的代码：

from Tkinter import *
import math

def calculate():
    try:
        num1 = float(enter1.get())
        num2 = float(enter2.get())
        result = num1 * num2
        label3.config(text=str(result))
    except ValueError:
        label3.config(text='Enter numeric values!', fg="white")

def calculate2():
    try:
        num1 = float(enter1.get())
        num2 = float(enter2.get())
        result = num1 / num2
        label3.config(text=str(result))
    except ValueError:
        label3.config(text='Enter numeric values!', fg="white")

def calculate3():
    try:
        num1 = float(enter1.get())
        num2 = float(enter2.get())
        result = num1 + num2
        label3.config(text=str(result))
   except ValueError:
        label3.config(text='Enter numeric values!',fg="white")

def calculate4():
    try:
        num1 = float(enter1.get())
        num2 = float(enter2.get())
        result = num1 - num2
        label3.config(text=str(result))
    except ValueError:
        label3.config(text='Enter numeric values!',fg="white")

def calculate5():
    try:
        num1 = float(enter1.get())
        result = num1**2
        label3.config(text=str(result))
    except ValueError:
        label3.config(text='Enter numeric values!',fg="white")

def calculate6():
    try:
        num1 = float(enter1.get())
        result = math.sqrt(num1)
        label3.config(text=str(result))
    except ValueError:
        label3.config(text='Enter numeric values!',fg="white")


root = Tk()
root.configure(background='black')
root.wm_title("Calc")

label1 = Label(root, text='First Number:',bg="black", fg="white")
label1.grid(row=0, column=0,columnspan=2)
enter1 = Entry(root, bg='white')
enter1.grid(row=1, column=0,columnspan=2)

label2 = Label(root, text='Second Number:',bg="black", fg="white")
label2.grid(row=2, column=0,columnspan=2)
enter2 = Entry(root, bg='white')
enter2.grid(row=3, column=0, columnspan=2)

btn1 = Button(root, text='-Multiply-', command=calculate,                                       bg="  black",activebackground="green", fg="white")
btn1.grid(row=4, column=0)
btn2 = Button(root, text='-Divide-', command=calculate2,  bg="black",activebackground="orange", fg="white")
btn2.grid(row=5, column=0)
btn3 = Button(root, text='-Add-', command=calculate3, bg="black",activebackground="purple", fg="white")
btn3.grid(row=5, column=1)
btn4 = Button(root, text='-Subtract-', command=calculate4, bg="black",activebackground="red", fg="white")
btn4.grid(row=4, column=1)
btn5 = Button(root, text='Square (Only First #)', command=calculate5, bg="black",activebackground="cyan", fg="white")
btn5.grid(row=6, column=0, columnspan=2)
btn6 = Button(root, text='Square Root (only First #)', command=calculate6, bg="black",activebackground="yellow", fg="white")
btn6.grid(row=7, column=0, columnspan=2,)
label3 = Label(root, bg="black")
label3.grid(row=8, column=0, columnspan=2)

enter1.focus()
enter1.bind('<Return>', func=lambda e:enter2.focus_set())
root.mainloop()

Answer 1

你的代码没有任何问题，唯一的问题是文本颜色最初是黑色的。这就是为什么它在显示错误之前“起作用”的原因，因为该选项将fg选项设置为白色，并且在接下来的更改中，它将保持已配置的相同文本颜色。在

要解决这个问题，只需在创建Label小部件时将fg选项设置为"white"：

label3 = Label(root, bg="black", fg="white")