mandelbrot error

Traceback (most recent call last):
  File "mandelbrot.py", line 49, in <module>
    curses.wrapper(main)
  File "/usr/lib/python3.5/curses/__init__.py", line 94, in wrapper
    return func(stdscr, *args, **kwds)
  File "mandelbrot.py", line 46, in main
    canvas.refresh(0,0, 0,0, Y-1,X-1)
_curses.error: prefresh() returned ERR