title: python argparse always set defaults related to an optional argument
body: <p>I use python 3, i want to set argparse to always set the default key in relation to a predefined optional argument of my choice.</p>
  
  <p>E.g. I pass some input files to the script. An optional argument specify if the input file should be rotated by the script. I get a list of input files but I also want a list of the same size containing 'True' where the user want to rotate the input file, or the default false when the user has not made a choice</p>
  
  <p>For example</p>
  
  <pre><code>import argparse
  parser = argparse.ArgumentParser()
  parser.add_argument('--input', action='append', required=True, help='Input pdf files.')
  parser.add_argument('--rotate', action='store_true', default=False, help='Rotate the input file')
  args = parser.parse_args()
  print(args)
  </code></pre>
  
  <p>I call the script with this command:</p>
  
  <pre><code>python argparse_test.py --input 1.pdf --input 2.pdf --rotate
  </code></pre>
  
  <p>This is the output</p>
  
  <blockquote>
    <p>Namespace(input=['1.pdf', '2.pdf'], rotate=True)</p>
  </blockquote>
  
  <p>But I want this output instead</p>
  
  <blockquote>
    <p>Namespace(input=['1.pdf', '2.pdf'], rotate=[False,True])</p>
  </blockquote>
  
  <p>Please note that <code>--rotate</code> can be ANY operation that must be performed by the python script i'm writing on the <code>--input</code> file before the <code>--rotate</code> itself. So i need to know which <code>--input</code> file <code>--rotate</code> is refering to</p>