title: Error when installing python3 packages in alpine
body: <p>I am currently building an image from alpine:3.7. </p>
  
  <p>There are two packages that I am having problems with:</p>
  
  <ul>
  <li>pendulum (specifically <strong>python-dateutils</strong> package)</li>
  <li>service_identity (specifically <strong>attrs</strong> package)</li>
  </ul>
  
  <p>The error that I receive it is: </p>
  
  <blockquote>
    <p>Could not find a version that satisfies the requirement setuptools (from versions: ) No matching distribution found for setuptools</p>
  </blockquote>
  
  <p>Note: all packages are pre-cached on a directory using pip download.</p>
  
  <p>The dockerfile looks as follows: </p>
  
  <pre><code>RUN apk add --no-cache --virtual .build-deps &lt;dev packages&gt;
   &amp;&amp; apk add --no-cache --update python3
   &amp;&amp; pip3 install --upgrade pip setuptools
  
  RUN pip3 install -f ./python-packages --no-index -r requirements.txt ./python-packages/pkgs
  
  ....
  </code></pre>
  
  <p>dev-packages such as libffi-dev, libressl-dev, etc.</p>