title: How to specify python version used to create Virtual Environment?
body: <p>My Python virtual environments use <code>python3.6</code> when I create them using <code>virtualenv</code></p>
  <blockquote>
  <p><code>~ $ virtualenv my_env</code></p>
  </blockquote>
  <p>but I need to use <code>python3.5</code> as 3.6 is <a href="https://github.com/menpo/conda-opencv3/issues/21" rel="noreferrer">not currently supported by <code>Opencv3</code>.</a></p>
  <p>I've tried using the <code>--python=&lt;py_version&gt;</code> flag when creating a virtual environment but this doesn't work.</p>
  <h1>How do I specify the python (3.x) version to install using <code>virtualenv</code> for Mac and/or Linux?</h1>