class_docstr: An environment for running on clusters with processes created through MPI.
  
  Requires the installation of the `mpi4py` package. See also: https://github.com/mpi4py/mpi4py
code: def world_size(self) -> int:
      return self._comm_world.Get_size()
  
imports: import logging
  import socket
  from functools import lru_cache
  from typing import Optional
  from lightning_utilities.core.imports import RequirementCache
  from typing_extensions import override
  from lightning.fabric.plugins.environments.cluster_environment import ClusterEnvironment
  from lightning.fabric.plugins.environments.lightning import find_free_network_port
label_desc: Use image node_id 6 for calling the MPIEnvironment obj's underlying member method code with example usage: obj.world_size() and returns: self