matplotlib backend issue

using different backends for matplotlib might cause some unexpected issues: today, i am trying to run a program that uses the following function:

plt.figure()
figManager = plt.get_current_fig_manager()
figManager.window.showMaximized()

however, i found when using the backend of Tk, it gives error, saying get_current_fig_manager is not available, so when i switch to qt4egg, everything works well.

how to switch the backend for matplotlib? first find the configure directory for matplotlib on your computer

import matplotlib as plt
plt.get_configdir()

then find/generate a file named matplotlibrc, add line:

backend      : qt4agg

reference here

another issue with using qt4 as backend is below from stackoverflow I was trying to use matplotlib to replot an image in a faster way, so instead of replotting everything, I use set_data method of the AxesImage class as below:

import numpy as np
import time
import matplotlib.pyplot as plt

fig, ax = plt.subplots()
img = plt.imshow(np.random.rand(100, 100))

img.set_data(np.random.rand(100, 100))
ax.draw_artist(ax.patch)
ax.draw_artist(img)
fig.canvas.update()
fig.canvas.flush_events()

I encountered this error:

Traceback (most recent call last): … ax.draw_artist(ax.patch) File “/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/matplotlib/axes/_base.py”, line 2319, in draw_artist raise AttributeError(msg) AttributeError: draw_artist can only be used after an initial draw which caches the render

However, if I run the script line by line in python shell (IPython), it works and nothing is wrong. So what is the mystery behind this cached renderer?

EDIT: add a line fig.canvas.draw() solves the problem, now the remaining question is why running it line by line in IPython shell does not cause the same error?