title: Why Sphinx does not find module 'sphinxcontrib.serializinghtml'
body: <p>Since I updated Sphinx from 1.7 to 2.2.0 an attempt to create the documentation ends at once with </p>
  
  <blockquote>
    <p>Could not import extension sphinx.builders.epub3 (exception: No module
    named 'sphinxcontrib.serializinghtml')</p>
  </blockquote>
  
  <p>I am starting Sphinx from pyCharm 2018.2 under Windows 7 Enterprise SP1 with Python 3.7. Environment variable "Path" contains the path to python 37, python 37/lib, python 37/lib/site-packages, python 37/dlls. The module serializinghtml exists in "Python 37\Lib\site-packages\sphinxcontrib\".</p>
  
  <p>Can anybody help please?</p>
  
  <p>Best regards 
  Humbalan</p>