code: def lookup(cls, leaderPath):
          
          pathHash = cls._pathHash(leaderPath)
          try:
              path_key = cls.resourceEnvNamePrefix + pathHash
              s = os.environ[path_key]
          except KeyError:
              log.warn("'%s' may exist, but is not yet referenced by the worker (KeyError from os.environ[]).", str(path_key))
              return None
          else:
              self = cls.unpickle(s)
              assert self.pathHash == pathHash
              return self
docs: Returns a resource object representing a resource created from a file or directory at the
          given path on the leader. This method should be invoked on the worker. The given path
          does not need to refer to an existing file or directory on the worker, it only identifies
          the resource within an instance of toil. This method returns None if no resource for the
          given path exists.
  
          :rtype: Resource