title: No activate_this.py file in venv / pyvenv
body: <p>I need to start venv / pyvenv from within a python script and I know the official documentation is to run:</p>
  
  <pre><code>activate_this = '/path/to/env/bin/activate_this.py'
  execfile(activate_this, dict(__file__=activate_this))
  </code></pre>
  
  <p>But I don't have an activate_this.py file and I can't find anywhere how to create one.</p>
  
  <p>I am running python 3.4.1. Any idea what I need to do?</p>