from tkinter import *
window = Tk()
window.title("Программирование циклических алгоритмов")
window.geometry("650x450")
f_ish = Frame(window)
f_ish = LabelFrame(text="Исходные данные", font=("Times new Roman",14))
lbl = Label(f_ish, text="Ввод левой границы интервала:", font=("Times new Roman", 14))
lbl.grid(column=0, row=0)
txt1 = Entry(f_ish, width=18, font=("Times new Roman", 14))
txt1.grid(column=2, row=0)
lbl1 = Label(f_ish, text="Ввод правой границы интервала:", font=("Times new Roman", 14))
lbl1.grid(column=0, row=1)
txt2 = Entry(f_ish, width=18, font=("Times new Roman", 14))
txt2.grid(column=2, row=1)
lbl2 = Label(f_ish, text="Ввод количества чисел последовательности:", font=("Times new Roman", 14))
lbl2.grid(column=0, row=2)
txt3 = Entry(f_ish, width=18, font=("Times new Roman", 14))
txt3.grid(column=2, row=2)
lbl3 = Label(f_ish, text="Ввод чисел последовательности:", font=("Times new Roman", 14))
lbl3.grid(column=0, row=4)
txt5 = Text(f_ish, width=18, height=10, font=("Times new Roman", 14))
txt5.grid(column=2, row=4)
f_res = Frame(window)
f_res = LabelFrame(text="Результаты вычислений", font=("Times new Roman", 14))
lbl = Label(f_res, text="Сумма чисел последовательности:", font=("Times new Roman", 14),width=35)
lbl.grid(column=0, row=0)
txt6 = Entry(f_res, width=18, font=("Times new Roman", 14))
txt6.grid(column=1, row=0)
def clicked():
    a = int(txt1.get())
    b = int(txt2.get())
    n = int(txt3.get())
    sum = 0
    for i in range(1, n + 1):
        x = float(txt5.get(1.0+i,str(1.0+i)+" line-end"))
    if x > 0 and (x > b or x < a):
        sum = sum + x
    txt6.delete(0,END)
    txt6.insert(0,sum)
def clicked1():
    window.destroy()
f_but = Frame(window)
btn = Button(f_but, text="Расчет", width=25, command=clicked, font=("Times new Roman", 14))
btn.grid(column=0, row=1)
btn = Button(f_but, text="Выход", width=25, command=clicked1, font=("Times new Roman", 14))
btn.grid(column=0, row=2)
f_ish.pack()
f_res.pack()
f_but.pack()
window.mainloop()
/code
Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\Users\russt\AppData\Local\Programs\Python\Python39\lib\tkinter\__init__.py", line 1892, in __call__
    return self.func(*args)
  File "C:\Users\russt\PycharmProjects\pythonProject\main.py", line 35, in clicked
    x = float(txt5.get(1.0+i,str(1.0+i)+" line-end"))
  File "C:\Users\russt\AppData\Local\Programs\Python\Python39\lib\tkinter\__init__.py", line 3711, in get     
    return self.tk.call(self._w, 'get', index1, index2)
_tkinter.TclError: bad text index "2.0 line-end"

[code python]между этими тегами вставить код для правильного отображения [/code]

  
def clicked():
    txt6.delete(0, 'end')
    text = txt5.get('1.0', 'end')
    print(text) # так смотрим промежуточные значения
    res = sum(map(int, text.split(',')))
    print(res)
    txt6.insert(0, str(res))