title: source credentials from within python
body: <p>I thought of using the following to run a normally-run-as-shell inside python:</p>
  
  <pre><code>x = subprocess.call('source credentials.txt', shell=True)
  print os.environ
  </code></pre>
  
  <p>However, it seems that the environment doesn't update in the rest of the script. Why not? And is there a way to get over this with using shell (and not python) to update my os vars?</p>