title: Python argparse with multiple actions within one argument
body: <p>I'm trying to solve a problem with python's <strong>argparse</strong> function</p>
  
  <p>What I would like to achieve is, that if -k argument is specified, it's set to its default value (let's say 5), however if -k=3 is set, 'k' now contains 3...</p>
  
  <p>Here is an example:</p>
  
  <pre><code>python3 test.py -k
  </code></pre>
  
  <p>Namespace(k==5)</p>
  
  <pre><code>python3 test.py -k=3
  </code></pre>
  
  <p>Namespace(k==3)</p>
  
  <p>Is it possible to get something like this ? </p>
  
  <p>test.py</p>
  
  <pre><code>import argparse
  parser = argparse.ArgumentParser()
  parser.add_argument('-k ', metavar='n', type=int, default=5, dest='number')
  args = parser.parse_args()
  print(args)
  </code></pre>
  
  <p>Thanks in advance</p>