On Jun 24, 4:19 pm, schickb <[EMAIL PROTECTED]> wrote: > On Jun 24, 3:45 pm, Matimus <[EMAIL PROTECTED]> wrote: > > > > > > I think it would be useful if iterators on sequences had the __index__ > > > method so that they could be used to slice sequences. I was writing a > > > class and wanted to return a list iterator to callers. I then wanted > > > to let callers slice from an iterator's position, but that isn't > > > supported without creating a custom iterator class. > > > Could you post an example of what you are talking about? I'm not > > getting it. > > Interactive mock-up: > > >>> a = ['x','y','z'] > >>> it = iter(a) > >>> a[it:] > ['x', 'y', 'z'] > >>> it.next() > 'x' > >>> a[it:] > ['y', 'z'] > >>> a[:it] > ['x'] > >>> it.next() > 'y' > >>> a[it:] > > ['z'] > > This lets you use sequence iterators more general position indicators. > Currently if you want to track a position and slice from a tracked > position you must do it manually with an integer index. It's not > difficult, but given that sequence iterators already do that already > it seems redundant (and of course more error prone). > > > In any case, the first step is writing a PEP.http://www.python.org/dev/peps/ > > Ok thanks, but I do want some idea of interest level before spending a > bunch of time on this. > > -Brad
I have no problem with being able to query the position (state) of an iterator without changing its state. I think using the iterator itself as the index or part of a slice in the original sequence is non- obvious and also less useful than just a new method to query state. "Explicit is better than Implicit". I would rather see just `it.index()` or `it.state()` than the new specialized behavior implied by `it.__index__()`. I'm leaning towards `state` because sequences already have an `index` method, and two methods of the same name with different behaviors may be confusing. This gives you essentially the same ability, and the code seems a little more obvious IMHO. >>> a = ['x','y','z'] >>> it = iter(a) >>> a[it.state():] ['x', 'y', 'z'] >>> it.next() 'x' >>> a[it.state():] ['y', 'z'] >>> a[:it.state()] ['x'] >>> it.next() 'y' >>> a[it.state():] ['z'] >>> it.state() 2 Matt -- http://mail.python.org/mailman/listinfo/python-list
