title: Python dataclasses, correct way to default_factory a list of default dicts containing lists?
body: <p>I'd like to accomplish an init of a list, containing default dicts, in turn containing lists.</p>
  <p>What I have tried:</p>
  <pre class="lang-py prettyprint-override"><code>@dataclass
  class MyClass:
      self.b: int
      
      cache: list = field(default_factory=list) 
  
      def __post_init__(self):
          self.cache = [defaultdict(list) for _ in range(self.b)]
  
  </code></pre>
  <p>I'd appreciate help. Thank you.</p>