On 10月17日, 下午11时56分, Arnaud Delobelle <arno...@googlemail.com> wrote: > On Oct 17, 3:40 pm, StarWing <weasley...@sina.com> wrote: > > > > > hello everyone, I'm new here :-) > > > sometimes I want to iterate a part of a sequence. but don't want to > > copy it. i.e. > > > a = list(...) > > # now a is a list, and a[:] is another list, and so a[m:n] > > # now we do something with the 0~len(a)-3 elements of a > > for val in a[:-2]: > > #do something.... > > > but, this will cause a copy on a, has some convenience way to get a > > iter to iterate on a part of list? > > > i made this: > > class iterslice: > > def __init__(self, list): > > self.list = list > > > def __len__(self): > > return len(self.list) > > > def __getitem__(self, slice): > > import itertools > > listlen = len(self.list) > > range = (((slice.start + listlen) % listlen) if slice.start > > else 0, > > ((slice.stop + listlen) % listlen) if slice.stop else > > listlen, > > slice.step) > > return itertools.islice(self.list, *range) > > > a = [1,2,3,4] > > for i in iterslice(a)[:-1:2]: > > print i > > > my question is: > > - are there any *Standard* way to do this? (a buit-in function? a > > module?) > > - are there any better implements? > > > thanks for attention :-) > > Check the itertools module. > > HTH > > -- > Arnaud
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...:-( -- http://mail.python.org/mailman/listinfo/python-list
