Save an animation at the final step as a figure - python-2.7

Question

I wrote a script which animates the results I obtained, using matplotlib.
Besides the animation I got, I wanted to save the figure at the final step of the animation; just before the animation is repeated. I defined a save-flag, to avoid the figure being saved over and over. You can see the simplified version of my code below:
#!/usr/bin/env python
import numpy as np
from matplotlib import pyplot as plt
import matplotlib.animation as animation
x = np.array(range(12))
y = np.array([i**2 for i in range(12)])
fig = plt.figure()
ax = plt.axes(xlim = (0,15), ylim = (0,150))
line, = ax.plot([],[], 'o-')
def init():
line.set_data([], [])
return line,
save_flag = False
def animate(i):
i = (i+1)%(len(x)+1)
line.set_data(x[0:i], y[0:i])
global save_flag
if (save_flag == False) and (i == (len(x)-1)):
print "\nThe figure is being saved!\n"
fig.savefig("foo" + ".png")
save_flag = True
return line,
ani = animation.FuncAnimation(fig, animate, repeat=True, blit=True, init_func=init)
plt.show()
If you run the script, you will probably see that, at the end of the first loop, the the animation becomes erroneous. This error is due to the blit, which is set True. However, if it is set to False, then the figure repeats itself as it should be.
Why is there such a problem; could it be a bug? (My Python version is 2.7.5+.)
Is there a better way to save a figure at the end of an animation?