title: Python 3.7 cmath module import error
body: <p>i installed python3.7 on ubuntu using ppa:deadsnakes/ppa repository.</p>
  
  <p>When I try to run</p>
  
  <pre><code>import cmath
  </code></pre>
  
  <p>in python shell it fails with message:</p>
  
  <pre><code>ModuleNotFoundError: No module named 'cmath'
  </code></pre>
  
  <p>I didn't find any info about depracation of this library or anything in python3.7 changelog. It works fine in pythons 3.5 and 2.7. I tried installing it on different ubuntu virtual machines and computers and I always get the same result.</p>
  
  <p>Do I need to install some specific library or something (which I doubt because the module is listed in standard library <a href="https://docs.python.org/3/library/index.html" rel="nofollow noreferrer">https://docs.python.org/3/library/index.html</a>) or is problem elsewhere?</p>