title: python argparse - How to prevent by using a combination of arguments
body: <p>In argparse, I want to prevent a particular combination of arguments. Lets see the sample code.</p>
  <h2>Sample:</h2>
  <pre><code>import argparse
  
  parser = argparse.ArgumentParser(add_help=False)
  parser.add_argument('--firstname', dest='fn', action='store')
  parser.add_argument('--lastname', dest='ln', action='store')
  parser.add_argument('--fullname', dest='full', action='store')
  args = parser.parse_args()
  </code></pre>
  <p>For eg: <code>--firstname --lastname --fullname</code></p>
  <p>The user can run the code in 2 days.</p>
  <h2>Way 1:</h2>
  <pre><code>code.py --firstname myfirst --lastname mylast
  </code></pre>
  <h2>Way 2:</h2>
  <pre><code>code.py --fullname myfullname
  </code></pre>
  <h2>Prevent</h2>
  <p>We should not use the combination <code>fistname, fullname</code> or <code>lastname, fullname</code>. If we use both, then it should not execute.</p>
  <p>Can someone help me to fix this?</p>