import matplotlib.pyplot as plt

fig = plt.figure()
ax1 = fig.add_subplot(1,1,1)
ax2 = ax1.twinx()
ax2.cla()
ax1.plot([1,2,3])
fig.savefig('test.png')

import matplotlib.pyplot as plt

fig = plt.figure()
ax1 = fig.add_subplot(1,1,1)
ax2 = ax1.twinx()
ax1.plot([1,2,3])
fig.savefig('test.png')

$ python --version
Python 3.4.2 :: Continuum Analytics, Inc.
$ python -c 'import matplotlib; print(matplotlib.__version__)'
1.4.2