[Python-ideas] Pass a function as the argument "step" of range()

[Paul Moore]

On 4 July 2015 at 00:53, Andrew Barnert via Python-ideas
<python-ideas at python.org> wrote:
> Also, this has the same problem as many of the other proposed solutions, in that it assumes that you can transform the iterative n*2 into an analytic 2**n, and that you can work out the maximum domain value (10) in your head from the maximum range value (1000), and that both of those transformations will be obvious to the readers of the code. In this particular trivial case, that's true, but it's hard to imagine any real-life case where it would be.

One thing that I have kept stumbling over when I've been reading this
discussion is that I keep expecting there to be a "simple" (i.e.,
builtin, or in a relatively obvious module) way of generating repeated
applications of a single-argument function:

    def iterate(fn, start):
        while True:
            yield start
            start = fn)start)

... and yet I can't find one. Am I missing it, or does it not exist?
It's not hard to write, as shown above, so I'm not claiming it "needs
to be a builtin" necessarily, it just seems like a useful building
block.

Paul