title: Multiprocessing find process index?
body: <p>Let's say we use <code>multiprocessing.Pool(n)</code>, is there a ways to find which of the <code>n</code> processes we're in?
  To illustrate: In the following snippet I'd like to find a way to know what index of the process the <code>job</code> function is. I'm not talking about the process number of the system, just a local enumeration of the processes spawned by <code>Pool</code>.</p>
  <pre><code>from multiprocessing import Pool
  def job(x):
      process_idx = None # index 1,2,3,4?
      print(f'job {x} process {process_idx}')
  with Pool(4) as p:
      p.imap(job, range(10))
  </code></pre>