from tkinter import *
from tkinter import ttk


def calculate(*args):
    try:
        value = (numbers.get())
        sum_list.set(sum(list(map(int,value.split()))))
    except ValueError:
        pass
root = Tk()
root.title("Sum of the list")

mainframe = ttk.Frame(root, padding="3 3 12 12")
mainframe.grid(column=0, row=0, sticky=(N, W, E, S))
mainframe.columnconfigure(0, weight=1)
mainframe.rowconfigure(0, weight=1)

numbers = StringVar()
sum_list = StringVar()

numbers_entry = ttk.Entry(mainframe, width=7, textvariable=numbers)
numbers_entry.grid(column=2, row=1, sticky=(W, E))

ttk.Label(mainframe, textvariable=sum_list).grid(column=2, row=2, sticky=(W, E))
ttk.Button(mainframe, text="Calculate", command=calculate).grid(column=3, row=3, sticky=W)


ttk.Label(mainframe, text="numbers").grid(column=3, row=1, sticky=W)
ttk.Label(mainframe, text="sum up to").grid(column=1, row=2, sticky=E)
ttk.Label(mainframe, text="total").grid(column=3, row=2, sticky=W)

numbers_entry.focus()
root.bind('<Return>', calculate)
root.mainloop()