This is a simpler proposal born out of https://bugs.python.org/issue31815: adding __length_hint__ implementations to some known-infinite iterators in itertools that always raise TypeError.

This means that iterator consumers that use the operator.length_hint() API will throw an error when asked to consume them, rather than entering an uninterruptible infinite loop.

The proposed methods added by this proposal would be:

* itertools.count.__length_hint__
* itertools.cycle.__length_hint__
* itertools.repeat.__length_hint__

Each of these would raise TypeError (to indicate an explicitly non-finite length), rather than returning the default of 0 (which length hint API consumers typically interpret as indicating an unknown-but-finite length)