Matplotlib draw_artist(axis.patch) 在 MacOSX 后端失败

Question

我正在关注Speeding up Matplotlib -- Bastibe，通过仅更新图中已更改的内容来测试制作动画。我正在使用 MacPorts 安装的 Mac OS X 10.11.4、Python 3.4。代码如下：

'''Import modules'''
import matplotlib.pyplot as plt
import numpy as np
import time

'''Initialize figure and axis, perform first draw on canvas'''
fig, ax = plt.subplots()
line, = ax.plot(np.random.randn(100))
plt.show(block=False)
fig.canvas.draw()

'''Count how many plots made within 1 second'''
tstart = time.time()
num_plots = 0
while time.time()-tstart < 1:            # within 1 second
    line.set_ydata(np.random.randn(100)) # update line
    ax.draw_artist(ax.patch)             # draw background
    ax.draw_artist(line)                 # draw line
    fig.canvas.update()                  # update canvas
    fig.canvas.flush_events()
    num_plots += 1                       # count++
print(num_plots)

此代码在带有 Python 3.4 + Qt5Agg 后端的 Ubuntu 14.04 上运行良好。但在 Mac 上，它会报告

Traceback (most recent call last):
  File "./test.py", line 19, in <module>
    ax.draw_artist(ax.patch)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/matplotlib/axes/_base.py", line 2340, in draw_artist
    a.draw(self._cachedRenderer)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/matplotlib/artist.py", line 61, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/matplotlib/patches.py", line 486, in draw
    gc = renderer.new_gc()
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/matplotlib/backends/backend_macosx.py", line 99, in new_gc
    self.gc.save()
RuntimeError: CGContextRef is NULL

欢迎提出任何建议！

Answer 1

您需要使用不同的后端。 将这些行添加到脚本的开头：

import matplotlib

matplotlib.use('Qt4Agg')

这给了我 283 个图，而 fig.canvas.draw() 只给了 26 个图。