title: type=dict in argparse.add_argument()
body: <p>I'm trying to set up a dictionary as optional argument (using argparse); the following line is what I have so far:</p>
  
  <pre><code>parser.add_argument('-i','--image', type=dict, help='Generate an image map from the input file (syntax: {\'name\': &lt;name&gt;, \'voids\': \'#08080808\', \'0\': \'#00ff00ff\', \'100%%\': \'#ff00ff00\'}).')
  </code></pre>
  
  <p>But running the script:</p>
  
  <pre><code> $ ./script.py -i {'name': 'img.png','voids': '#00ff00ff','0': '#ff00ff00','100%': '#f80654ff'}
  
  script.py: error: argument -i/--image: invalid dict value: '{name:'
  </code></pre>
  
  <p>Even though, inside the interpreter,</p>
  
  <pre><code>&gt;&gt;&gt; a={'name': 'img.png','voids': '#00ff00ff','0': '#ff00ff00','100%': '#f80654ff'}
  </code></pre>
  
  <p>works just fine.</p>
  
  <p>So how should I pass the argument instead?
  Thanks in advance.</p>