Code for middle frame

# create frame to hold the middle row of widgets:
rframe = Frame(top)
# this frame (row) is packed from top to bottom:
rframe.pack(side='top')

# create label and entry in the frame and pack from left:
r_label = Label(rframe, text='The sine of')
r_label.pack(side='left')

r = StringVar()  # variable to be attached to widgets
r.set('1.2')     # default value
r_entry = Entry(rframe, width=6, relief='sunken', textvariable=r)
r_entry.pack(side='left')