old_contents: 
  import os
  import ConfigParser
  
  __all__ = ["Config"]
  
  Config = ConfigParser.RawConfigParser()
  
  if os.environ.get("PLOW_CFG"):
      Config.read([os.environ["PLOW_CFG"]])
  else:
      Config.read(["/etc/plow/plow.cfg", os.path.expanduser("~/.plow/plow.cfg")])
  
  def get(section, key):
      """
      Return the specified configuration option.  Automatically
      interpolates any environement variables specified in plow.ini.
      """
      interps = Config.get("env", "interpolate").split(",")
      args = dict([(inter, os.environ.get(inter, "test")) for inter in interps])
  
      result = Config.get(section, key)
      return result % args
  
  
   
new_contents: 
  import os
  import ConfigParser
  
  __all__ = ["Config"]
  
  Config = ConfigParser.RawConfigParser()
  
  if os.environ.get("PLOW_CFG"):
      Config.read([os.environ["PLOW_CFG"]])
  else:
      Config.read(["/etc/plow/plow.cfg", os.path.expanduser("~/.plow/plow.cfg")])
  
  assert Config.has_section("plow")
  
  def get(section, key):
      """
      Return the specified configuration option.  Automatically
      interpolates any environement variables specified in plow.ini.
      """
      interps = Config.get("env", "interpolate").split(",")
      args = dict([(inter, os.environ.get(inter, "test")) for inter in interps])
  
      result = Config.get(section, key)
      return result % args
  
  
   
subject: Add assertion so plow bails if not config is found.