code: def load_import_keychain( cls, working_dir, namespace_id ):
          
        
          # do we have a cached one on disk?
          cached_keychain = os.path.join(working_dir, "%s.keychain" % namespace_id)
          if os.path.exists( cached_keychain ):
  
              log.debug("Load import keychain '%s'" % cached_keychain)
              child_addrs = []
              try:
                  lines = []
                  with open(cached_keychain, "r") as f:
                      lines = f.readlines()
   
                  child_attrs = [l.strip() for l in lines]
   
                  log.debug("Loaded cached import keychain for '%s'" % namespace_id)
                  return child_attrs
   
              except Exception, e:
                  log.exception(e)
                  log.error("FATAL: uncaught exception loading the import keychain")
                  os.abort()
   
          else:
              log.debug("No import keychain at '%s'" % cached_keychain)
  
          return None
docs: Get an import keychain from disk.
          Return None if it doesn't exist.