title: Python package import from parent directory
body: <p>I've the following source code structure</p>
  
  <pre><code>/testapp/
  /testapp/__init__.py
  /testapp/testmsg.py
  /testapp/sub/
  /testapp/sub/__init__.py
  /testapp/sub/testprinter.py
  </code></pre>
  
  <p>where <code>testmsg</code> defines the following constant:</p>
  
  <pre><code>MSG = "Test message"
  </code></pre>
  
  <p>and <code>sub/testprinter.py</code>:</p>
  
  <pre><code>import testmsg
  
  print("The message is: {0}".format(testmsg.MSG))
  </code></pre>
  
  <p>But I'm getting <code>ImportError: No module named testmsg</code></p>
  
  <p>Shouldn't it be working since the package structure? I don't really want to extend sys.path in each submodule and I don't even want to use relative import.</p>
  
  <p>What am I doing wrong here?</p>