Tkinter使用类时出错 - TypeError: 不支持的操作数类型: 'DoubleVar'和'int

Question

你好，当我尝试从一个类获取一个 DoubleVar 类型的值，并把它和一个整数相乘时，出现了以下错误信息：

TypeError: unsupported operand type(s) for *: 'DoubleVar' and 'int'

我想从 quadratics 类中获取 vara、varb 和 varc 的值，然后在 quadratic_grapher 类中使用它们。

有没有人能帮我解决这个问题？

import matplotlib
matplotlib.use('TkAgg')
from matplotlib.backends.backend_tkagg import FigureCanvasTkAgg, NavigationToolbar2TkAgg
from matplotlib.backend_bases import key_press_handler
from matplotlib.figure import Figure
from tkinter import *
class home():
    def __init__(self,master):
        self.master = master
        self.master.geometry('400x450')
        self.master.title('Mathsolver')
        Button(self.master, text='Quadratics', command = self.open_quadratics).pack()
    def open_quadratics(self):
        quadratics(Toplevel(self.master))
class quadratics():
    def __init__(self, master):
        self.master = master
        self.vara = DoubleVar()
        self.varb = DoubleVar()
        self.varc = DoubleVar()
        self.master.geometry("500x300")
        self.master.title("Quadratic Equations")
        Label(self.master, text="Enter coefficients of x below in the form ax² + bx + c = 0").grid(row=1,column=1)
        Label(self.master, text="a:").grid(row=2,column=1)
        Entry(self.master, textvariable = self.vara).grid(row=2,column=2)
        Label(self.master, text="b:").grid(row=3,column=1)
        Entry(self.master, textvariable = self.varb).grid(row=3,column=2)
        Label(self.master, text="c:").grid(row=4,column=1)
        Entry(self.master, textvariable = self.varc).grid(row=4,column=2)
        Button(self.master, text="Solve", command = self.calculate_quadratic).grid(row=5,column=2)
        Button(self.master, text='Graph', command = self.grapher, bg='green').grid(row=5,column=2)
    def grapher(self):
           quadratic_grapher(Toplevel(self.master))
class quadratic_grapher(quadratics):
    def __init__(self, master):
        super(quadratic_grapher, self).__init__(master)
        self.master = master
        self.a_coefficient = self.vara
        self.b_coefficient = self.varb
        self.c_coefficient = self.varc
        f = Figure(figsize=(5,4), dpi=100)
        a = f.add_subplot(111)
        self.x1 = []
        self.y1 = []
        self.x2 = []
        self.y2 = []
        self.x_positive_increment = 1
        self.x_negative_decrement = -1
        self.x_positive = 0
        self.x_negative = 0
        for plotPoints in range(0, 10):
            self.y_positive = self.a_coefficient * self.x_positive**2 + self.b_coefficient * self.x_positive + self.c_coefficient
            self.y_negative = self.a_coefficient * self.x_negative**2 + self.b_coefficient * self.x_negative + self.c_coefficient
            self.x1.append(self.x_positive)
            self.x2.append(self.x_negative)
            self.y1.append(self.y_positive)
            self.y2.append(self.y_negative)
            self.x_positive = self.x_positive + self.x_positive_increment
            self.x_negative = self.x_negative + self.x_negative_decrement
        a.plot(self.x1, self.y1)
        a.plot(self.x2, self.y2)
        self.canvas = FigureCanvasTkAgg(f, master=master)
        self.canvas.show()
        self.canvas.get_tk_widget().pack(side=TOP, fill=BOTH, expand=1)
        self.toolbar = NavigationToolbar2TkAgg(self.canvas, master )
        self.toolbar.update()
        self.canvas._tkcanvas.pack(side=TOP, fill=BOTH, expand=1)
def main():
    root = Tk()
    home(root)
    root.mainloop()

if __name__ == '__main__':
    main()

Answer 1

a、b 和 c 这几个系数是一个叫做 变量类的实例。你可以用 .get() 方法来获取这个实例里的值。

下面是一个例子：

from tkinter import *

root = Tk()

var = DoubleVar()
var.set(1.0)

print(var.get())
print(var)

root.mainloop()