Ввод функции y = f(x) c Entry

from functions import inetration
from numpy import arange,sin
from tkinter import Tk,Label,Entry,Button
from matplotlib.pyplot import figure
from matplotlib.backends.backend_tkagg import FigureCanvasTkAgg
def calcul():
    a = float(textbox_1.get())
    b = float(textbox_2.get())
    lbl = Label(form , text = inetration(a,b,1e-5))
    lbl.place(x=300,y=300)
 
form = Tk()
form.title("LAB №3 (Inetration)")
form.geometry('400x450')
draw_button = Button(form, text="Рассчитать", command=calcul)
draw_button.place(x=20,y=400)
textbox_1 = Entry(form)
textbox_1.place(x=100,y=350)
textbox_2 = Entry(form)
textbox_2.place(x=100,y=300)
lbl_1 = Label(form, text="b =")
lbl_1.place(x=50,y=350)
lbl_2 = Label(form, text="a =")
lbl_2.place(x=50,y=300)
x = arange(-1.0,1.0,0.1)
y = sin(4.8*x)*5.67-4.5*x
graph = figure()
result = graph.add_subplot(1,1,1)
result.grid()
result.plot(x,y)
canvas = FigureCanvasTkAgg(graph, master=form)
canvas.get_tk_widget().grid()
form.mainloop()

from math import sin
from numpy import sign
from scipy.misc import derivative
def f(x):
    return sin(4.8*x)*5.67-4.5*x
def f1(x):
    return derivative(f, x, dx=1e-6)
def fi(x,lm):
    return x+lm*f(x)
 
def inetration(a,b,eps):
    if abs(f1(a))>1:
        l1=1/f1(a)
    else:
        l1=sign(f1(a))
    if abs(f1(b))>1:
        l2=1/f1(b)
    else:
        l2=sign(f1(b))
    if l1<l2:
        lm=-l1
    else:
        lm=-l2
    x0, i=(a+b)/2, 0
    x1=fi(x0,lm)
    while abs(x0-x1)>eps:
        x0=x1
        x1, i=fi(x0,lm),i+1
    str = ("x =%10.5f"%x1+"\ni =%3i"%i)
    return str