title: subprocess.Popen Argument list is too long
body: <p>I use </p>
  
  <pre><code>    proc = subprocess.Popen(cmd,
                              stdin=subprocess.PIPE,
                              stdout=subprocess.PIPE,
                              stderr=subprocess.STDOUT,
                              shell=shell,
                              universal_newlines=False,
                              env=env)
  </code></pre>
  
  <p>And the code fails with the exception</p>
  
  <pre><code> File "subprocess.py", line 623, in __init__
   File "subprocess.py", line 1141, in _execute_child
   OSError: [Errno 7] Argument list too long
  </code></pre>
  
  <p>I found that my command length was really huge and hence this fails. And now I have correct it. However, I'm trying to find what is the maximum length of the command string that I can pass to subprocess Popen.</p>