title: Why is List[str] not a subclass of Sequence[str]
body: <p><code>List</code> is a subclass of <code>Sequence</code>:</p>
  
  <pre><code>&gt;&gt;&gt; from typing import List, Sequence
  &gt;&gt;&gt; issubclass(List, Sequence)
  True
  </code></pre>
  
  <p>but <code>List[str]</code> is not a subclass of <code>Sequence[str]</code>:</p>
  
  <pre><code>&gt;&gt;&gt; issubclass(List[str], Sequence[str])
  False
  </code></pre>
  
  <p>Why?</p>