title: os.environ not setting environment variables
body: <p>I'm trying to set a Windows environment variable using Python.</p>
  
  <p>It seems that, contrary to the docs, <a href="https://docs.python.org/3.4/library/os.html#os.environ" rel="noreferrer">os.environ</a> can get environment variables but cannot set them. Try running these in a Windows Command Prompt:</p>
  
  <p>This works:</p>
  
  <pre><code>python -c "import os; print(os.environ['PATH'])"
  </code></pre>
  
  <p>This does not:</p>
  
  <pre><code>python -c "import os; os.environ['FOO'] = 'BAR'"
  </code></pre>
  
  <p>Try typing <code>set</code> in the Command Prompt. The environment variable FOO does not exist.</p>
  
  <p>How can I set a permanent Windows environment variable from Python?</p>