<h4 dir="auto">Description</h4>

<p dir="auto">Enter into the doc directory and try to make and generate pdf manual file, failed.</p>
<h4 dir="auto">Steps/Code to Reproduce</h4>

<ol dir="auto">
<li>Update the codebase to the latest version.</li>
<li>Enter into the "doc" directory, and type the cmd: make latexpdf</li>
<li>Wait after a while, errors will appear.</li>
</ol>
<h4 dir="auto">Expected Results</h4>

<p dir="auto">PDF file should be generated, at least should not be interrupted by the exceptions.</p>
<h4 dir="auto">Actual Results</h4>

<p dir="auto">The build process has been interrupted by the errors, following is the details:<br>
Traceback (most recent call last):<br>
File "/usr/local/lib/python2.7/dist-packages/sphinx/cmdline.py", line 306, in main<br>
app.build(opts.force_all, filenames)<br>
File "/usr/local/lib/python2.7/dist-packages/sphinx/application.py", line 357, in build<br>
self.emit('build-finished', None)<br>
File "/usr/local/lib/python2.7/dist-packages/sphinx/application.py", line 489, in emit<br>
return self.events.emit(event, self, *args)<br>
File "/usr/local/lib/python2.7/dist-packages/sphinx/events.py", line 79, in emit<br>
results.append(callback(*args))<br>
File "/usr/local/lib/python2.7/dist-packages/sphinx_gallery/gen_gallery.py", line 329, in sumarize_failing_examples<br>
"\n" + "-" * 79)<br>
ValueError: Here is a summary of the problems encountered when running the examples</p>
<p dir="auto">Unexpected failing examples:<br>
/home/kevin/research/openSource/scikit-learn-fork/examples/ensemble/plot_feature_transformation.py failed leaving traceb<br>
ack:<br>
Traceback (most recent call last):<br>
File "/home/kevin/research/openSource/scikit-learn-fork/examples/ensemble/plot_feature_transformation.py", line 37, in<br>
<br>
from sklearn.preprocessing import CategoricalEncoder<br>
ImportError: cannot import name CategoricalEncoder</p>
<p dir="auto">/home/kevin/research/openSource/scikit-learn-fork/examples/applications/plot_out_of_core_classification.py failed leavin<br>
g traceback:<br>
Traceback (most recent call last):<br>
File "/home/kevin/research/openSource/scikit-learn-fork/examples/applications/plot_out_of_core_classification.py", lin<br>
e 111<br>
end='')<br>
^<br>
SyntaxError: invalid syntax<br>
<a href="https://github.com/scikit-learn/scikit-learn/files/1515684/sphinx-err-M9XrCr.log">sphinx-err-M9XrCr.log</a></p>
<h4 dir="auto">Versions</h4>

<p dir="auto">Linux-4.4.0-43-Microsoft-x86_64-with-Ubuntu-16.04-xenial<br>
('Python', '2.7.12 (default, Nov 20 2017, 18:23:56) \n[GCC 5.4.0 20160609]')<br>
('NumPy', '1.13.3')<br>
('SciPy', '0.16.0')<br>
('Scikit-Learn', '0.20.dev0')</p>
<p dir="auto">We currently use Travis to run unit tests with various versions of dependencies, including python 2. But we only run the examples when building the docs in python 3 with Circle CI. <a class="issue-link js-issue-link" data-error-text="Failed to load title" data-id="265913081" data-permission-text="Title is private" data-url="https://github.com/scikit-learn/scikit-learn/issues/9936" data-hovercard-type="issue" data-hovercard-url="/scikit-learn/scikit-learn/issues/9936/hovercard" href="https://github.com/scikit-learn/scikit-learn/issues/9936">#9936</a> shows that this allows incompatible example code to be introduced, and I expect this to increase as more developers use python 3 though we still support python 2. Perhaps we should add a Travis run that builds the examples, whether or not it compiles the rest of the documentation.</p>