temp

def F_C():
    far=float(m.get())
    cel=round(((far-32)*5/9),2)
    n.set((str(far)+" = "+str(cel)))

from Tkinter import *

w=Tk()

m=StringVar()
m.set("")

dato=Entry(w,textvariable=m)
dato.pack()

b1=Button(w,text="F -> C", command=F_C)
b1.pack()

n=StringVar()
n.set("")

text=Label(w,textvariable=n)
text.pack()

w.mainloop()