title: Optional subparsers?
body: <p>I have a <a href="https://github.com/naftulikay/aws-env" rel="nofollow noreferrer">utility</a> which allows a user to read their <code>~/.aws/credentials</code> file and export environment variables.</p>
  
  <p>Currently, the CLI interface looks like this:</p>
  
  <pre><code>usage: aws-env [-h] [-n] profile
  
  Extract AWS credentials for a given profile as environment variables.
  
  positional arguments:
    profile          The profile in ~/.aws/credentials to extract credentials
                     for.
  
  optional arguments:
    -h, --help       show this help message and exit
    -n, --no-export  Do not use export on the variables.
  </code></pre>
  
  <p>What I'd like to do here is provide a <code>ls</code> subparser that will allow the user to list the valid profile names in their <code>~/.aws/credentials</code>. </p>
  
  <p>The interface would be something like this:</p>
  
  <pre><code>$ aws-env ls
  profile-1
  profile-2
  </code></pre>
  
  <p>...etcetera. Is there a way that I can natively do this in argparse so that an option appears in my <code>-h</code> output which shows that <code>ls</code> is a valid command?</p>