new_contents: # Thin wrapper around progressbar library
  #   http://code.google.com/p/python-progressbar/
  # Provides dummy wrapper if library is unavailable.
  
  try:
    from progressbar import *
  except ImportError:
    class ProgressBar(object):
      def __init__(self, *args, **kwargs): pass
      def start(self): pass
      def update(self, x): pass
      def finish(self): pass
  
subject: Add dummy implementation of progressbar if unavailable.