old_contents: from spath import shortest_path
  
new_contents: try:
      from spath import shortest_path
  except ImportError:
      print """*** The shortest path extension has not been compiled.  Run
  
  python setup.py build_ext -i
  
  in the source directory to build in-place.  Please refer to INSTALL.txt
  for further detail."""
  
subject: Allow importing even when not compiled.