user warning in flexure tutorial #2

at step 3 get this user warning:

/Users/jennyknuth/anaconda/lib/python2.7/site-packages/matplotlib/init.py:1350: UserWarning: This call to matplotlib.use() has no effect
because the backend has already been chosen;
matplotlib.use() must be called before pylab, matplotlib.pyplot,
or matplotlib.backends is imported for the first time.

warnings.warn(_use_error_msg)