matplotlib数字在show（）和savefig（）之间消失

Question

I've kept a set of references to figures in a dictionary so that I could save them later if desired. I am troubled that the saved figures are blank if invoke a show() command and look at them first. Since the show() command blocks and I am not using a spyder-like interpreter, I have to close the figures before I get to savefig()

figures['myfig_1'] = figure()
...
figures['myfig_n'] = figure()
...

#show() #disabling this makes the problem go away
print "Saving:"
for fig in figures:
   figure(figures[fig].number)
   savefig(fig)
   print "Figure " + str(figures[fig].number) + ": " + fig

The print statement here has given me the indication that the dictionary is still intact, which I think means that I have not lost the figure references (they are still returning meaningful numbers in their .number attribute.)

Another twist I have noticed is that when I have done a similar thing in a class, storing the dictionary as a member and dividing the store and save functions into their own methods, this does not happen. Is there something about the way I am closing the figures or storing the data which is making the figures loose their data?

Answer 1

Generally speaking, in cases like this don't use the interactive matlab-ish state machine interface to matplotlib. It's meant for interactive use.

You're trying to make a figure "active", and creating a new figure instead. It doesn't matter which figure is active, if you just retain the returned figure and/or axis objects and use them directly. (Also, don't use wildcard imports! You will regret it at some later point when you're maintaining your code!)

Just do something like this:

import matplotlib.pyplot as plt
figures = {}

figures['a'] = plt.figure()
ax = figures['a'].add_subplot(111)
ax.plot(range(10), 'ro-')

figures['b'] = plt.figure()
ax = figures['b'].add_subplot(111)
ax.plot(range(10), 'bo-')

plt.show()

for name, fig in figures.iteritems():
    fig.savefig('figure-%s.png' % name)

Answer 2

From the documentation , whether or not the drawing elements are destroyed from show() depends on the backend , and the version of matplotlib. Not having the figures destroyed seems to be available with version 1.1.0. To figure out which backend is in use , use the get_backend() function. In my case, I was using the Qt4Agg backend. By invoking the TkAgg backend, with the call matplotlib.use('TkAgg') the figures were not destroyed before the save. Now to find out how to change the behavior of the Qt4Agg...