title: How to prevent python from using orphaned .pyc files? (ones with no matching .py files)
body: <p>Once in a while I run into a very difficult-to-debug problem: there's a leftover .pyc file somewhere in my $PYTHONPATH, and the matching .py file has been moved to somewhere else that's later in $PYTHONPATH - so when I try to import the module, the "orphaned" .pyc file is used and all changes to the "real" .py file are ignored, leaving me incredibly confused until I figure out that's what's happening.  </p>
  
  <p>Is there any way of making python <em>not</em> use "orphaned" .pyc files, or print a warning when using them?<br>
  Alternatively, does the fact that I have this problem at all mean I'm doing something wrong, and if so, what?</p>