title: Mac OSX: Switch to Python 2.7.3
body: <p>I've installed the <a href="http://www.python.org/download/releases/2.7.3/" rel="noreferrer">Mac OSX Python 2.7.3</a>, and tried switching to the new version:</p>
  
  <pre class="lang-bash prettyprint-override"><code>$ python2.7 -V
  Python 2.7.3         # It was installed
  $ python -V
  Python 2.6.1         # Default is 2.6
  $ export VERSIONER_PYTHON_VERSION=2.5
  $ python -V
  Python 2.5.4         # I can switch to 2.5
  $ export VERSIONER_PYTHON_VERSION=2.6
  $ python -V
  Python 2.6.1         # And 2.6
  </code></pre>
  
  <p>But:
  </p>
  
  <pre><code>$ export VERSIONER_PYTHON_VERSION=2.7
  $ python -V
  python: VERSIONER_PYTHON_VERSION environment variable error (ignored)
  Python 2.6.1
  </code></pre>
  
  <p>Can't switch to 2.7! Why is that?</p>