title: what does argument "bound" mean in typing.TypeVar?
body: <p>So I am trying to learn typing module and I am completely stuck on <code>bound=</code> part.
  I've read <a href="https://stackoverflow.com/questions/59933946/difference-between-typevart-a-b-and-typevart-bound-uniona-b">this</a> comprehensive topic a couple a times, but since I am newbie to this I didn't understand much.</p>
  <p>Can you please explain what <code>bound=</code> is for and what does upper-bound means? (on a simple example preferably)</p>
  <p>Thank you beforehand!</p>