title: os.environ['PATH'] does not work when running Python code from command-line
body: <p>Why does the following not work?</p>
  
  <pre><code>$ python -c 'import os; print os.environ['PATH']'
  Traceback (most recent call last):
     File "&lt;string&gt;", line 1, in &lt;module&gt;
  NameError: name 'PATH' is not defined
  </code></pre>
  
  <p>whereas</p>
  
  <pre><code>$ python
  
  &gt;&gt;&gt; import os
  &gt;&gt;&gt; print os.environ['PATH']
  </code></pre>
  
  <p>works?</p>