RuntimeError: Failed to import pydot. You must install pydot and graphviz for `pydotprint` to work.

`Using TensorFlow backend.
Traceback (most recent call last):
File "mnist-cnn.py", line 14, in
from keras.utils.visualize_util import plot
File "/usr/local/lib/python2.7/dist-packages/keras/utils/visualize_util.py", line 13, in
raise RuntimeError('Failed to import pydot. You must install pydot'

RuntimeError: Failed to import pydot. You must install pydot and graphviz for pydotprint to work.`

上記のエラーが出た時

sudo apt-get install graphviz
pip install graphviz
pip install pydot==1.1.0
を行った。

on Ubuntu 16.04.