Re: [Matplotlib-users] RuntimeError: CGContextRef is NULL

[Friedrich R. <fri...@gm...>]

2010/10/4 Nicolas Rougier <Nic...@lo...>:
> I'm trying to have animated plots using draw_artist on mac os x and I got an error with the following script:
>
> import numpy as np
> import matplotlib.pyplot as plt
>
> plt.ion()
> plt.figure()
> subplot = plt.subplot(1,1,1)
> axis = plt.imshow(np.random.random((10,10)))
> plt.draw()
> subplot.draw_artist(axis)
> plt.show()
>
> The traceback is:
>
> Traceback (most recent call last):
>  File "matplotlib-bug.py", line 8, in <module>
>    subplot.draw_artist(axis)
>  File "/Volumes/Data/Local/lib/python2.7/site-packages/matplotlib/axes.py", line 1946, in draw_artist
>    a.draw(self._cachedRenderer)
>  File "/Volumes/Data/Local/lib/python2.7/site-packages/matplotlib/artist.py", line 55, in draw_wrapper
>    draw(artist, renderer, *args, **kwargs)
>  File "/Volumes/Data/Local/lib/python2.7/site-packages/matplotlib/image.py", line 338, in draw
>    gc = renderer.new_gc()
>  File "/Volumes/Data/Local/lib/python2.7/site-packages/matplotlib/backends/backend_macosx.py", line 105, in new_gc
>    self.gc.save()
> RuntimeError: CGContextRef is NULL
>
>
> Is there something wrong in my script (it seems to be working on linux) ?

I don't know what it is, and it looks like some problem with the
Mac-native backend, but I believe you can sort it out by just
switching the backend to e.g. TkAgg.

Friedrich