Могу ли я получить математическую функцию из Entry?

import matplotlib.pyplot as plt  
import numpy as np  # Array do Python
from math  import sqrt, pi

class WNN(object):
    def __init__(self, eta=0.008, epoch_max=4000, Ni=1, Nh=40, Ns=1):
        ### Inijalizacja parametrów
        self.eta = eta
        self.epoch_max = epoch_max
        self.Ni = Ni
        self.Nh = Nh
        self.Ns = Ns
        self.Aini = 0.01




    def load_first_function(self,d):
        self.d =d 
        x = np.arange(-6, 6, 0.15)
        self.N = x.shape[0]
        xmax = np.max(x)

        self.X_train = x / xmax
        self.d = 1 / (1 + np.exp(-1 * x))*(np.cos(x) - np.sin(x))
        #self.d = np.sin(x)
        #self.d= np.cos(x)
        #self.d = np.cos(x)*np.sin(x)
        #self.d = 1 / (1 + np.exp(-1 * x))
        #self.d=(np.cos(x) - np.sin(x))



    def sig_dev2(self, theta):
        return 2*(1 / (1 + np.exp(-theta)))**3 - 3*(1 / (1 + np.exp(-theta)))**2 + (1 / (1 + np.exp(-theta)))

    def sig_dev3(self, theta):
        return -6*(1 / (1 + np.exp(-theta)))**4 + 12*(1 / (1 + np.exp(-theta)))**3 - 7*(1 / (1 + np.exp(-theta)))**2 + (1 / (1 + np.exp(-theta)))

    def sig_dev4(self, theta):
        return 24*(1 / (1 + np.exp(-theta)))**5 - 60*(1 / (1 + np.exp(-theta)))**4 + 50*(1 / (1 + np.exp(-theta)))**3 - 15*(1 / (1 + np.exp(-theta)))**2 + (1 / (1 + np.exp(-theta)))

    def sig_dev5(self, theta):
        return -120*(1 / (1 + np.exp(-theta)))**6 + 360*(1 / (1 + np.exp(-theta)))**5 - 390*(1 / (1 + np.exp(-theta)))**4 + 180*(1 / (1 + np.exp(-theta)))**3 - 31*(1 / (1 + np.exp(-theta)))**2 + (1 / (1 + np.exp(-theta)))

    def train(self):
        ### Inicjalizacja wag
        self.A = np.random.rand(self.Ns, self.Nh) * self.Aini

        ### Inicjalizacja centrów
        self.t = np.zeros((1, self.Nh))

        idx = np.random.permutation(self.Nh)
        for j in range(self.Nh):
            self.t[0,j] = self.d[idx[j]]

        ### Szerokość wczytywania
        self.R = abs(np.max(self.t) - np.min(self.t)) / 2

        MSE = np.zeros(self.epoch_max)
        plt.ion()

        for epoca in range(self.epoch_max):
            z = np.zeros(self.N)
            E = np.zeros(self.N)

            index = np.random.permutation(self.N)

            for i in index:
                xi = self.X_train[i]#np.array([self.X_train[i]]).reshape(1, -1)
                theta = (xi - self.t) / self.R
                yj = self.sig_dev2(theta)
                z[i] = np.dot(self.A, yj.T)[0][0]

                e = self.d[i] - z[i]
                self.A = self.A + (self.eta * e * yj)
                self.t = self.t - (self.eta * e * self.A / self.R * self.sig_dev3(theta))
                self.R = self.R - (((self.eta * e * self.A * (xi - self.t)) / self.R**2) * self.sig_dev3(theta))

                E[i] = 0.5 * e**2

            MSE[epoca] = np.sum(E) / self.N

            if (epoca % 200 == 0 or epoca == self.epoch_max - 1):
                if (epoca != 0):
                    plt.cla()
                    plt.clf()

                self.plot(z, epoca)

        print (MSE[-1])

        plt.ion()




    def plot(self, saida, epoca):
        plt.figure(0)
        y, = plt.plot(self.X_train, saida, label="y")
        d, = plt.plot(self.X_train, self.d, '.', label="d")
        plt.legend([y, d], ['WNN Output', 'Desired Value'])
        plt.xlabel('x')
        plt.ylabel('f(x)')
        plt.text(np.min(self.X_train) - np.max(self.X_train) * 0.17  , np.min(self.d) - np.max(self.d) * 0.17, 'Progress: ' + str(round(float(epoca) / self.epoch_max * 100, 2)) + '%')
        plt.axis([np.min(self.X_train) - np.max(self.X_train) * 0.2, np.max(self.X_train) * 1.2, np.min(self.d) - np.max(self.d) * 0.2, np.max(self.d) * 1.4])
        plt.show()
        plt.pause(1e-100)

    def show_function(self):
        plt.figure(0)
        plt.title('Function')
        plt.xlabel('x')
        plt.ylabel('f(x)')
        plt.plot(self.X_train, self.d)
        plt.show()
    wnn = WNN()
x = np.arange(-6, 6, 0.15)
wnn.load_first_function(np.sin(x))
wnn.train()    
%matplotlib
    import tkinter
    from tkinter import *
    from tkinter import ttk
    window = Tk()
    window.title("Approximation")
    window.resizable(0, 0)
    window.geometry('350x200')
    ##For leraning rate
    lbl = Label(window, text="Write lr")
    lbl.grid(column=0, row=0)
    txt = Entry(window,width=10)
    txt.grid(column=1, row=0)
    ##For epochs
    lbl2 = Label(window, text="Write epochs")
    lbl2.grid(column = 0,row=1)
    txt2=Entry(window,width=10)
    txt2.grid(column=1, row=1)
    ##For hidden neurons
    lbl3 = Label(window, text="Write neurons")
    lbl3.grid(column = 0,row=2)
    txt3=Entry(window,width=10)
    txt3.grid(column=1, row=2)
    #For functions
    lbl4=Label(window,text = "Write your function")
    lbl4.grid(column = 0,row = 3)
    txt4=Entry(window,width= 10)
    txt4.grid(column=1,row=3)

    combo=ttk.Combobox(window,values=["np.sin(x)"])
    combo.grid(column=1,row=3)
    d=combo.get()
    combo.current(0)
    epoch_max = txt2.get()
    eta = txt.get()
    Nh = txt3.get()
    btnChange=Button(window,text="Save options",command=lambda:[wnn.__init__(eta = float(txt.get()) ,epoch_max = int(txt2.get()) , Nh=int(txt3.get()),Ni=1, Ns=1),wnn.load_first_function(d=str(combo.get()))])
    btnChange.grid(column =2,row = 2)

    def plot(self, saida, epoca):
            plt.figure(0)
            y, = plt.plot(self.X_train, saida, label="y")
            d, = plt.plot(self.X_train, self.d, '.', label="d")
            plt.legend([y, d], ['WNN Output', 'Desired Value'])
            plt.xlabel('x')
            plt.ylabel('f(x)')
            plt.text(np.min(self.X_train) - np.max(self.X_train) * 0.17  , np.min(self.d) - np.max(self.d) * 0.17, 'Progress: ' + str(round(float(epoca) / self.epoch_max * 100, 2)) + '%')
            plt.axis([np.min(self.X_train) - np.max(self.X_train) * 0.2, np.max(self.X_train) * 1.2, np.min(self.d) - np.max(self.d) * 0.2, np.max(self.d) * 1.4])
            plt.show()
            plt.pause(1e-100)
    btn = Button(window, text="Start", command=lambda:wnn.train(),height=5,width = 10)
    btn.grid(column=4, row=4)
    window.mainloop()

Из кода выше видно, что в данный момент я могу взять число из Entry. Но как я могу взять математическую функцию? Или есть другой способ получения функции от пользователя?