title: How do i know if a subprocess has started or not?
body: <p>I have the following subprocess.</p>
  
  <pre><code>ss = subprocess.Popen(["python3", "-m", "unittest", totest], 
                        stdin=None, 
                        stdout=subprocess.PIPE,  
                        stderr=subprocess.PIPE)
  </code></pre>
  
  <p>I want to know if it has started or it had thrown errors.</p>