title: python equivalent of functools 'partial' for a class / constructor
body: <p>I want to create a class that behaves like collections.defaultdict, without having the usage code specify the factory. EG:
  instead of </p>
  
  <pre><code>class Config(collections.defaultdict):
      pass
  </code></pre>
  
  <p>this:</p>
  
  <pre><code>Config = functools.partial(collections.defaultdict, list)
  </code></pre>
  
  <p>This almost works, but </p>
  
  <pre><code>isinstance(Config(), Config)
  </code></pre>
  
  <p>fails. I am betting this clue means there are more devious problems deeper in also. So is there a way to actually achieve this?</p>
  
  <p>I also tried:</p>
  
  <pre><code>class Config(Object):
      __init__ = functools.partial(collections.defaultdict, list)
  </code></pre>