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On Fri, Nov 16, 2018 at 7:57 AM Steve Keller <keller at no.invalid> wrote: > > I have looked at generators, generator expressions, and iterators and > I try to get more familiar with these. > > 1. How would I loop over all (with no upper bound) integers or all > powers of two, for example? > > In C it would be > > for (int i = 0; ; i++) { ... } or for (int i = 1; ; i *= 2) { ... } > > In Python, I could define a generator > > def powers(): > i = 1 > while True: > yield(i) > i *= 2 > > for i in powers(): > ... > > More elegant are generator expressions but I cannot think of a way > without giving an upper limit: > > for i in (2 ** i for i in range(1000000)): > ... > > which looks ugly. Also, the double for-loop (and also the two loops > in the above exmaple, for + while in the generator) look unnatural, > somehow, i.e. loop over all elements which are created by a loop. > > Is there a more beautyful way? Some options: from itertools import count def powers(): for i in count(): yield 2 ** i for i in (2 ** i for i in count()): ... for i in map(lambda x: 2 ** x, count()): ... from functools import partial from operator import pow for i in map(partial(pow, 2), count()): ... Take your pick.

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