Python GUI计算器（退格键和加号/减号）

Question

我正在使用Python GUI创建一个简单的计算器，并且已完成所有工作，但是我无法弄清楚如何为def Backspace（self）和def Plusminus（self）编写代码：

现在，退格按钮正在删除数字或功能，但并未存储该数字或功能，您按下的所有下一个按钮都将返回。

如果数字大于0，则正号/负号应该使数字为负；如果数字小于0，则正号/负号应使之为正。现在，它只是在前面加上一个负号，而实际上并未使数字为负。

from tkinter import *

class Application(Frame):


def __init__(self, master):

    super(Application, self).__init__(master)
    self.task = ""
    self.UserIn = StringVar()
    self.grid()
    self.create_widgets()

def create_widgets(self):
    #Create all the buttons for calculator.
    # User input stored as an Entry widget.

    self.user_input = Entry(self, bg = "White",
    insertwidth = 4, width = 24,
    font = ("Times", 20), textvariable = self.UserIn, justify = RIGHT)
    self.user_input.grid(columnspan = 4)

    self.user_input.insert(0, "0")

    # Button for value 7
    self.button1 = Button(self, bg = "White",
    text = "7", padx = 40, pady = 20, font = ("Times", 20),
    command = lambda : self.buttonClick(7))
    self.button1.grid(row = 2, column = 0, sticky = W)

    # Button for value 8
    self.button2 = Button(self, bg = "White",
    text = "8",  padx = 40, pady = 20,
    command = lambda : self.buttonClick(8), font = ("Times", 20))
    self.button2.grid(row = 2, column = 1, sticky = W)

    # Button for value 9
    self.button3 = Button(self, bg = "White",
    text = "9",  padx = 40, pady = 20,
    command = lambda : self.buttonClick(9), font = ("Times", 20))
    self.button3.grid(row = 2, column = 2, sticky = W)

    # Button for value 4
    self.button4 = Button(self, bg = "White",
    text = "4",  padx = 40, pady = 20,
    command = lambda : self.buttonClick(4), font = ("Times", 20))
    self.button4.grid(row = 3, column = 0, sticky = W)

    # Button for value 5
    self.button5 = Button(self, bg = "White",
    text = "5",  padx = 40, pady = 20,
    command = lambda : self.buttonClick(5), font = ("Times", 20))
    self.button5.grid(row = 3, column = 1, sticky = W)

    # Button for value 6
    self.button6 = Button(self, bg = "White",
    text = "6",  padx = 40, pady = 20,
    command = lambda : self.buttonClick(6), font = ("Times", 20))
    self.button6.grid(row = 3, column = 2, sticky = W)

    # Button for value 1
    self.button7 = Button(self, bg = "White",
    text = "1",  padx = 40, pady = 20,
    command = lambda : self.buttonClick(1), font = ("Times", 20))
    self.button7.grid(row = 4, column = 0, sticky = W)

    # Button for value 2
    self.button8 = Button(self, bg = "White",
    text = "2",  padx = 40, pady = 20,
    command = lambda : self.buttonClick(2), font = ("Times", 20))
    self.button8.grid(row = 4, column = 1, sticky = W)

    # Button for value 3
    self.button9 = Button(self, bg = "White",
    text = "3",  padx = 40, pady = 20,
    command = lambda : self.buttonClick(3), font = ("Times", 20))
    self.button9.grid(row = 4, column = 2, sticky = W)

    # Button for value 0
    self.button9 = Button(self, bg = "White",
    text = "0",  padx = 40, pady = 20,
    command = lambda : self.buttonClick(0), font = ("Times", 20))
    self.button9.grid(row = 5, column = 0, sticky = W)

    # Operator buttons
    # Addition button
    self.Addbutton = Button(self, bg = "White",
    text = "+",  padx = 20, pady = 20,
    command = lambda : self.buttonClick("+"), font = ("Times", 20))
    self.Addbutton.grid(row = 2, column = 3, sticky = W)

    # Subtraction button
    self.Subbutton = Button(self, bg = "White",
    text = "-",  padx = 23, pady = 20,
    command = lambda : self.buttonClick("-"), font = ("Times", 20))
    self.Subbutton.grid(row = 3, column = 3, sticky = W)

    # Multiplication button
    self.Multbutton = Button(self, bg = "White",
    text = "*",  padx = 20, pady = 20,
    command = lambda : self.buttonClick("*"), font = ("Times", 20))
    self.Multbutton.grid(row = 4, column = 3, sticky = W)

    # Division button
    self.Divbutton = Button(self, bg = "White",
    text = "/",  padx = 23, pady = 20,
    command = lambda : self.buttonClick("/"), font = ("Times", 20))
    self.Divbutton.grid(row = 5, column = 3, sticky = W)

    # Equal button
    self.Equalbutton = Button(self, bg = "White",
    text = "=",  padx = 98, pady = 20,
    command = self.CalculateTask, font = ("Times", 20))
    self.Equalbutton.grid(row = 5, column = 1, sticky = W, columnspan = 2)

    # Clear Button
    self.Clearbutton = Button(self, bg = "White",
    text = "C", font = ("Times", 20), padx = 38, pady = 20, command = self.ClearDisplay)
    self.Clearbutton.grid(row = 1, columnspan = 2, sticky = W)

    # Backspace Button
    self.Backspace = Button(self, bg = "White",
    text = "<",  padx = 20, pady = 20,
    command = self.Backspace, font = ("Times", 20))
    self.Backspace.grid(row = 1, column = 3, sticky = W)

    # Blank Button
    self.blank = Button(self, bg = 'White',
    text = ' ', padx = 44, pady = 20,
    font = ('Times', 20))
    self.blank.grid(row = 1, column = 1, sticky = W)

    # +/- Button
    self.Plusminus = Button(self, bg = 'White',
    text = '+/-', padx = 31, pady = 20,
    command = self.Plusminus, font = ('Times', 20))
    self.Plusminus.grid(row = 1, column = 2, sticky = W)

def buttonClick(self, number):
    self.task = str(self.task) + str(number)
    self.UserIn.set(self.task)

def CalculateTask(self):
    self.data = self.user_input.get()
    try:
        self.answer = eval(self.data)
        self.displayText(self.answer)
        self.task = self.answer

    except SyntaxError as e:
        self.displayText("Invalid Syntax!")
        self.task = ""

def displayText(self, value):
    self.user_input.delete(0, END)
    self.user_input.insert(0, value)

def ClearDisplay(self):
    self.task = ""
    self.user_input.delete(0, END)
    self.user_input.insert(0, "0")

def Backspace(self):
    self.data = self.user_input.get()
    self.user_input.delete(len(self.data)-1, END)

def Plusminus(self):
    self.data = self.user_input.get()
    if self.data.startswith('-'):
        self.user_input.delete(0, 1) # delete the first character

    else:
        self.user_input.insert(0, '-') # add a - to the front
    print(self.data)
    print(self.task)

calculator = Tk()

calculator.title("My Calculator")
app = Application(calculator)
# Make window fixed (cannot be resized)
calculator.resizable(width = False, height = False)

calculator.mainloop()

Answer 1

问题在于您不更新self.task变量，而只修改用户输入字符串。

在self.user_input.insert(0, '-')之后的self.user_input.insert(0, '-')

self.task = self.user_input.get()

Backspace（）中的同上。

我还注意到您使用self.Plusminus作为函数和小部件的变量名。 实际上， self.Plusminus首先引用该函数，而在创建小部件时，其后引用它。 现在这不会给您造成问题，您应该避免这种情况。