title: Regular Expression '[\w-]+(\.[\w-]+)*' doesn't get matched
body: <p>I want to process some sentences in the document of PostgreSQL and do some analysis. In the word spliting stage, I tried to use the regex <strong>'[\w-]+(.[\w-]+)*'</strong> proposed by Lotufo et al. in the article <em>Modelling the Hurried bug report reading process to summarize
  bug reports</em>. It's quite strange that I cann't get the expected answer using this regex in Python. </p>
  
  <pre class="lang-py prettyprint-override"><code>Python 3.6.5 |Anaconda, Inc.| (default, Mar 29 2018, 13:32:41) [MSC v.1900 64 bit (AMD64)]
  Type "copyright", "credits" or "license" for more information.
  
  IPython 6.4.0 -- An enhanced Interactive Python.
  &gt;&gt;&gt; import re
  &gt;&gt;&gt; result = re.findall(r'[\w-]+(\.[\w-]+)*', 'Specifies the directory to use for data storage.')
  &gt;&gt;&gt; print(result)
  </code></pre>
  
  <p>I expected to get a list of words：</p>
  
  <pre><code>['Specifies', 'the', 'directory', 'to', 'use', 'for', 'data', 'storage']
  </code></pre>
  
  <p>But I only got a list of empty string:</p>
  
  <pre><code>['', '', '', '', '', '', '', '']
  </code></pre>
  
  <p>Does any one have any idea what is wrong with my code? Thanks a lot.</p>