class_docstr: Describe the environment inside which the job is running.
  This includes job id, number of GPUs available, ...
  
  This class can only be instantiated from a running submitit job.
  
  @plugin-dev: default implementation look for information into environment variables.
  Override _env to map environment variable to each property.
docstr: Total number of nodes for the job
code: def num_nodes(self) -> int:
      """Total number of nodes for the job"""
      return int(os.environ.get(self._env["num_nodes"], 1))
  
imports: import os
  import signal
  import socket
  import sys
  import time
  import types
  import typing
  from pathlib import Path
  from .None import logger, utils
  from .utils import DelayedSubmission, JobPaths
label_desc: Use image node_id 13 for calling the JobEnvironment obj's underlying member method code with example usage: obj.num_nodes() and returns: int