title: how to understand os.environ['JOB_ID'] in python
body: <p>I have this piece of code from python.</p>
  
  <pre><code>if _name_ == '_main_':
     dir, file = os.path.split("myfile.csv")
     out_dir = os.path.join(dir, "myoutput-{0}".format(os.environ['JOB_ID']))
  </code></pre>
  
  <p>I found it is not easy to understand the very last line, especially the <code>os.environ['JOB_ID']</code> part. After searching, this may belong to the SGE game engine of python. But I notice that in the python file, there are no statements like "import sge". I am confused. Can anyone please help? Many thanks for your time and attention. </p>