http://bugs.python.org/review/27689/diff/18074/Doc/library/typing.rst File Doc/library/typing.rst (right): http://bugs.python.org/review/27689/diff/18074/Doc/library/typing.rst#newcod... Doc/library/typing.rst:474: while sent is not None: One more comment: One might be confused why send type is float and not Optional[float], maybe you could add an explanation that one anyway can only send None as a first value, so that Optional is redundant. http://bugs.python.org/review/27689/