importnumpyasnpimportmatplotlib.pyplotaspltx=y=np.linspace(-5,5)x,y=np.meshgrid(x,y)z=x**2+y**2-10plt.rcParams['contour.negative_linestyle']= [7.0,7.0]f=plt.figure()plt.contour(x,y,z,colors='k',levels=20)f.savefig('test.eps')

Traceback (most recent call last):  File "<ipython-input-12-d73b5c362b1b>", line 1, in <module>    f.savefig('test.eps')  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\figure.py", line 2180, in savefig    self.canvas.print_figure(fname, **kwargs)  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\backends\backend_qt5agg.py", line 88, in print_figure    super().print_figure(*args, **kwargs)  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\backend_bases.py", line 2082, in print_figure    **kwargs)  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\backends\backend_ps.py", line 842, in print_eps    return self._print_ps(outfile, 'eps', *args, **kwargs)  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\backends\backend_ps.py", line 871, in _print_ps    **kwargs)  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\backends\backend_ps.py", line 966, in _print_figure    self.figure.draw(renderer)  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\artist.py", line 38, in draw_wrapper    return draw(artist, renderer, *args, **kwargs)  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\figure.py", line 1709, in draw    renderer, self, artists, self.suppressComposite)  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\image.py", line 135, in _draw_list_compositing_images    a.draw(renderer)  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\artist.py", line 38, in draw_wrapper    return draw(artist, renderer, *args, **kwargs)  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\axes\_base.py", line 2647, in draw    mimage._draw_list_compositing_images(renderer, self, artists)  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\image.py", line 135, in _draw_list_compositing_images    a.draw(renderer)  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\artist.py", line 38, in draw_wrapper    return draw(artist, renderer, *args, **kwargs)  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\collections.py", line 329, in draw    self._offset_position)  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\backends\backend_ps.py", line 492, in draw_path_collection    offset_position)  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\backend_bases.py", line 245, in draw_path_collection    self.draw_path(gc0, path, transform, rgbFace)  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\backends\backend_ps.py", line 414, in draw_path    self._draw_ps(ps, gc, rgbFace)  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\backends\backend_ps.py", line 759, in _draw_ps    self.set_linedash(*gc.get_dashes())  File "C:\Users\mhossein\Anaconda3\lib\site-packages\matplotlib\backends\backend_ps.py", line 276, in set_linedash    s = "[%s] %d setdash\n" % (_nums_to_str(*seq), offset)TypeError: %d format: a number is required, not NoneType