title: Cython compilation using wrong Mac OS libraries
body: <p>I'm working on a project built with Cython and have been having some interesting installation issues on some particular systems.  The problem boils down to either a mismatch in Mac OS versions, or a mismatch in my understanding of Mac OS versions.</p>
  
  <p>When installing a Cython library on my system, the compilation log shows that I am using Mac OS version 10.12, even though my system tells me I am on 10.13. An excerpt of the compilation log is below:</p>
  
  <pre><code>creating build/temp.macosx-10.12-x86_64-3.6
  </code></pre>
  
  <p>This is not a problem for me, but another user is having trouble where their system release on 10.13, but their compilation is showing 10.7 (which requires some other work arounds).</p>
  
  <p>Is it possible to update this build system? Or is there something about Mac OS that I'm misunderstanding? </p>
  
  <p>Is there a way to tell from a Python script which build libraries will be used?</p>
  
  <p>Thank you!</p>
  
  <p><strong>Edit:</strong></p>
  
  <p>Output of platform information:</p>
  
  <pre><code>&gt;&gt;&gt; python -c "import platform; print(platform.mac_ver())"
  ('10.13.6', ('', '', ''), 'x86_64')
  
  &gt;&gt;&gt; python -c "import distutils.util; print(distutils.util.get_platform())"
  macosx-10.12-x86_64
  </code></pre>