On 10月18日, 上午9时09分, Raymond Hettinger <pyt...@rcn.com> wrote: > [StarWing] > > > > > sometimes I want to iterate a part of a sequence. but don't want to > > > > copy it. i.e. > . . . > > I had checked it for serval times. maybe it's my inattention :-(. but > > what i could find the nearest thing is itertools.islice. but it can't > > process negative index -- that's supported by slice. so I need > > something, bind object with slice, and return a iter. I can find > > anything like it...:-( > > If it really is a sequence (with len and getitem), you can write your > own indexing iterator: > > def myslice(seq, start, stop, step): > 'Allow forward or backwards iteration over a subslice' > for i in range(start, stop, step): > yield seq[i] > > Raymond
Thank you. but it can't support negative index :-( Terry Reedy is right. since a range (or xrange or slice etc.) don't have a length, so it can't support a negative index. so the best way to do it is that binding a range with a object. and return a iter. I think, why standard library didn't have anything like that, that will be very useful. maybe we should have a builtin functoin itertools.bslice (stands for bind slice)... -- http://mail.python.org/mailman/listinfo/python-list
