title: Flag to not require mandatory arguments in Argparse?
body: <p>I have a program that accepts input file, input format, and output format as required arguments via argparse. However, I'd like to have "--test" as a flag, where it will run through all of my unit tests. </p>
  
  <p>How do I set this to be a flag that can run without the required arguments? In the same way that a traditional -h flag does?</p>
  
  <pre class="lang-py prettyprint-override"><code>def process_args():
      global args
      parser = argparse.ArgumentParser(description="Convert quantum circuits into different environments")
      parser.add_argument("input_filename", help="input filename")
      parser.add_argument("input_format", help="input format of your script", choices=valid_program_types)
      parser.add_argument("output_format", help="output format of your script", choices=valid_program_types)
      parser.add_argument("-o", "--output_filename", help="set output filename, without file extension "
                                                          "(default: convertqc_result.&lt;filetype&gt;")
      parser.add_argument("-d", "--debug", help="enable debug mode", action="store_true")
      args = parser.parse_args()
  </code></pre>