import matplotlib
matplotlib.use('MacOSX')
import matplotlib.pyplot as plt

fig, ax = plt.subplots()
fig.savefig('test.png')

  File "test.py", line 6, in <module>
    fig.savefig('test.png')
  File "/Users/dstansby/github/matplotlib/lib/matplotlib/figure.py", line 1813, in savefig
    self.canvas.print_figure(fname, **kwargs)
  File "/Users/dstansby/github/matplotlib/lib/matplotlib/backend_bases.py", line 2258, in print_figure
    **kwargs)
  File "/Users/dstansby/github/matplotlib/lib/matplotlib/backends/backend_agg.py", line 507, in print_png
    FigureCanvasAgg.draw(self)
  File "/Users/dstansby/github/matplotlib/lib/matplotlib/backends/backend_agg.py", line 429, in draw
    toolbar.set_cursor(cursors.WAIT)
  File "/Users/dstansby/github/matplotlib/lib/matplotlib/backends/backend_macosx.py", line 188, in set_cursor
    _macosx.set_cursor(cursor)
SystemError: <built-in function set_cursor> returned NULL without setting an error