from tkinter import *
import math

root = Tk()     
top = Frame(root)
top.pack(side='top')

hwframe = Frame(top)
hwframe.pack(side='top')
font = 'times 18 bold'
hwtext = Label(hwframe, text='Hello, World!', font=font)
hwtext.pack(side='top', pady=20)

rframe = Frame(top)
rframe.pack(side='top', padx=10, pady=20)
r_label = Label(rframe, text='The sine of')
r_label.pack(side='left')
r = StringVar()
r.set('1.2')   
r_entry = Entry(rframe, width=6, textvariable=r)
r_entry.pack(side='left')

s = StringVar()
def comp_s(event):
    global s
    s.set('%g' % math.sin(float(r.get()))) # construct string

r_entry.bind('<Return>', comp_s)

compute = Label(rframe, text=' equals ')
compute.pack(side='left')

s_label = Label(rframe, textvariable=s, width=12)
s_label.pack(side='left')

def quit(event=None):
    root.destroy()

quit_button = Button(top, text='Goodbye, GUI World!', command=quit,
                     background='yellow', foreground='blue')
quit_button.pack(side='top', pady=5, fill='x')

root.bind('<q>', quit)

root.mainloop()