title: matplotlib save animation in gif error
body: <p>I want to save matplotlib animation in gif format.</p>
  
  <p>I succeded to save animation to mp4 format, using code</p>
  
  <pre><code>import matplotlib
  matplotlib.use("Agg")
  
  ~some codes~
  
  ani = animation.FuncAnimation(fig, draw, update, interval=10, blit=False)
  mywriter = animation.FFMpegWriter(fps=60)
  ani.save('myanimation.mp4',writer=mywriter)
  </code></pre>
  
  <p>but if I change myanimation.mp4 to gif format, python makes error </p>
  
  <pre><code>Traceback (most recent call last):
    File "C:\Users\Administrator\Desktop\edison\Edison_v4_backup_1\ver5.py", line 164, in &lt;module&gt;
      ani.save('demoanimation.gif',writer=mywriter);
    File "C:\Python27\lib\site-packages\matplotlib\animation.py", line 718, in save
      writer.grab_frame(**savefig_kwargs)
    File "C:\Python27\lib\site-packages\matplotlib\animation.py", line 204, in grab_frame
      dpi=self.dpi, **savefig_kwargs)
    File "C:\Python27\lib\site-packages\matplotlib\figure.py", line 1421, in savefig
      self.canvas.print_figure(*args, **kwargs)
    File "C:\Python27\lib\site-packages\matplotlib\backend_bases.py", line 2220, in print_figure
      **kwargs)
    File "C:\Python27\lib\site-packages\matplotlib\backends\backend_agg.py", line 497, in print_raw
      renderer._renderer.write_rgba(filename_or_obj)
  RuntimeError: Error writing to file
  </code></pre>
  
  <p>Seeing that I succeded to save in mp4 format, I don't know why it makes error when saving gif format.</p>