Fate of itertools.dropwhile() and itertools.takewhile()

[Raymond Hettinger]

I'm considering deprecating these two functions and would like some
feedback from the community or from people who have a background in
functional programming.

* I'm concerned that use cases for the two functions are uncommon and
can obscure code rather than clarify it.

* I originally added them to itertools because they were found in
other functional languages and because it seemed like they would serve
basic building blocks in combination with other itertools allow
construction of a variety of powerful, high-speed iterators.  The
latter may have been a false hope -- to date, I've not seen good
recipes that depend on either function.

* If an always true or always false predicate is given, it can be hard
to break-out of the function once it is running.

* Both functions seem simple and basic until you try to explain them
to someone else.  Likewise, when reading code containing dropwhile(),
I don't think it is self-evident that dropwhile() may have a lengthy
start-up time.

* Since itertools are meant to be combined together, the whole module
becomes easier to use if there are fewer tools to choose from.

These thoughts reflect my own experience with the itertools module.
It may be that your experience with them has been different.  Please
let me know what you think.

Raymond