title: What is the meaning of __total__ dunder attribute in Python 3?
body: <p>In newly released Python 3.8 there is a new type annotation <a href="https://docs.python.org/3.8/library/typing.html#typing.TypedDict" rel="noreferrer"><code>typing.TypedDict</code></a>. Its documentation mentions that</p>
  
  <blockquote>
    <p>The type info for introspection can be accessed via <code>Point2D.__annotations__</code> and <code>Point2D.__total__</code>. [....]</p>
  </blockquote>
  
  <p>While <code>__annotations__</code> is well-known, having been introduced in <a href="https://www.python.org/dev/peps/pep-3107/" rel="noreferrer">PEP 3107</a>, I cannot find any information on <code>__total__</code>. Could anyone explain its meaning and if possible linking to authoritative sources?</p>