[housecarpenter]

I used generators with return values once when writing a lexer. I had generators for each of a bunch of different states of the lexer (e.g. skipping over whitespace, reading a numeric literal, reading a string literal, etc.). Each generator would yielded the tokens that it could and then either return one of the other generators (if a state transition was required) or None (if it reached the end of the input and the state was one where this wasn't an error condition). The whole thing was tied together with this function:

  def lex(src):
    state = skip_whitespace

    while state is not None:
      state = yield from state()

It wasn't particularly essential to use the return value from the generator here, as I could have just made the state variable available in the scope of the state functions for them to mutate, but this seemed like a cleaner way to do it as it enforced the idea that each new state corresponded to a new function.