Hi Steve, I tried this when writing DocCron <https://github.com/Code-ReaQtor/DocCron>but it will not work correctly.
Suppose we have minutes with range 0-59 and seconds with range 0-59 but starting at, say, 5: When the seconds value reaches 59, on the next iteration the minute value should increase by 1 (or back to zero) but it will not work that way since the next rotation will be at 4 transitioning to 5. So the correct solution is not modifying any of the arrangements. Best Regards, Ronie On Thu, Oct 25, 2018 at 7:31 PM Steven D'Aprano <st...@pearwood.info> wrote: > On Thu, Oct 25, 2018 at 02:31:05PM +0800, Ronie Martinez wrote: > > > def main(): > > datetime_odometer = itertools.product( > > range(2018, 10_000), # year > > range(1, 13), # month > > range(1, 31), # days > > range(0, 24), # hours > > range(0, 60), # minutes > > range(0, 60) # seconds > > ) > > When you talked about datetime, I thought you meant actual datetime > objects. The above is buggy: it ignores the 31st day of January, etc, > but includes February 29 and 30 every year. > > > > datetime_of_interest = (2050, 6, 15, 10, 5, 0) > > > > for i in datetime_odometer: > > if i == datetime_of_interest: # target start time > > break > > In the most general case, there is no way to jump into the middle of an > arbitrary iterator, except to start at the beginning and compute the > values until you see the one that you want. Arbitrary iterators compute > their values on request, and there is no way to jump ahead except by > inspecting each value in turn, skipping the ones you don't want. > > So unless I have missed something, I think what you are asking for is > impossible except for special cases like lists. > > But in *this* case, modelling an odometer, that special case works: > > def rotate(iterable, position): > L = list(iterable) > return L[position:] + L[:position] > > Which gives us this: > > py> months = rotate(range(1, 13), 5) > py> months > [6, 7, 8, 9, 10, 11, 12, 1, 2, 3, 4, 5] > > Now pass that to itertools.product. > > In other words, I think that the right solution here is to construct > your iterables to start at the position you want, rather than expect > product() to jump into the middle of the sequence. (Which may not be > possible.) > > > > -- > Steve > _______________________________________________ > Python-ideas mailing list > Python-ideas@python.org > https://mail.python.org/mailman/listinfo/python-ideas > Code of Conduct: http://python.org/psf/codeofconduct/ >
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