title: Is Python3 shlex.quote() safe?
body: <p>I execute some code in shell using </p>
  
  <pre><code>subprocess.Popen('echo '+user_string+' | pipe to some string manipulation tools',
      shell=True)
  </code></pre>
  
  <p>where user_string is from an untrusted source.</p>
  
  <p>Is it safe enough to use <code>shlex.quote()</code> for escaping the input?</p>