code: def chained_get(self, *keys):
          
          existing = self
          for i in range(0, len(keys)):
              if keys[i] in existing:
                  existing = existing[keys[i]]
              else:
                  return None
          return existing
docs: This function allows traversals over several keys to
          be performed by passing a list of keys::
  
              d.chained_get(key1,key2,key3) = d[key1][key2][key3]