code: def lookup(self, lsid):
          
          if self.registered_modules is None or lsid not in self.registered_modules:
              return None
          else:
              return self.registered_modules[lsid]
docs: Look up the name of a module by LSID assigned by the authority.
          Returns None if the LSID is not found.
          :param lsid:
          :return: string or none