from Tkinter import *

r = Tk()

def onReturnKey(event): 
    print 'Got return key press\n' + text.get()
    
    f = open('/home/luke/sync/to-do.txt', 'a')
    f.write('\n' + text.get())
    f.close()
    
    r.quit()


text = Entry(r)

h=15
w=150
ws = r.winfo_screenwidth()
hs = r.winfo_screenheight()
x = (ws/2) - (w/2)
y = (hs/2) - (h/2)
r.geometry('%dx%d+%d+%d' % (w, h, x, y))

text.pack()
text.focus()
r.title('Enter thought:')

r.bind('<Return>', onReturnKey)
r.mainloop()