title: Import from sibling directory
body: <p>I have a Python class called "ClassA" and another Python class which is supposed to import ClassA which is "ClassB". The directory structure is as follows:</p>
  
  <pre><code>MainDir
  ../Dir
  ..../DirA/ClassA
  ..../DirB/ClassB
  </code></pre>
  
  <p>How would I use <code>sys.path</code> so that ClassB can use ClassA?</p>