Why is pip install pyopenssl==0.13 failing?
<p>I'm trying to install PyOpenSSL 0.13 on my Macbook Pro (OSX version 10.11, El-Capitan). But it keeps failing. These are the steps I took</p>

<ol>
<li>Download and install Command Line Tools (OSX 10.11) for Xcode 7.3.1 from <a href="https://developer.apple.com/download/more/" rel="nofollow">here</a></li>
<li><code>$ virtualenv my-new-virtualenv</code></li>
<li><code>$ source my-new-virtualenv/bin/activate</code></li>
<li><code>$ pip install pyopenssl==0.13</code></li>
</ol>

<p>When I do step #4, I get the following error:</p>

<pre><code>OpenSSL/crypto/x509.h:17:10: fatal error: 'openssl/ssl.h' file not found
  #include &lt;openssl/ssl.h&gt;
       ^
  1 error generated.
  error: command 'cc' failed with exit status 1

  ----------------------------------------
  Failed building wheel for pyopenssl
</code></pre>

<p><a href="https://gist.github.com/saqib-zmi/ce8894cd8c40599bc886608dbbf1c9ce" rel="nofollow"><strong>Here</strong></a> is the entire trace showing that error.</p>

<p>Why am I getting this error and how can I fix it??</p>