"Bengt Richter" <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] > On Wed, 26 Jan 2005 11:55:59 -0800, jfj <[EMAIL PROTECTED]> wrote: > > >Jeff Shannon wrote: > > > >> > >> > >> So, what problem is it, exactly, that you think you'd solve by making > >> tuple slices a view rather than a copy? > >> > > > >I think views are good for > > 1) saving memory > > 2) saving time (as you don't have to copy the elements into the new tuple) > > > >And they are worth it. However, (as in other cases with slicing), it is > >very easy and fast to create a view for a slice with the default step > >'1', while it's a PITA and totally not worth it to create a view for a > >slice with non default step. I think it would be good to: > > > > if slice_step == 1 > > create_view > > else > > create_new_tuple > > > >Actually, i think that slices with step, is a bad feature in general > >and i think I will write a PEP to suggest their removal in python3k. > > > What's the big deal with other than 1 steps? It is just adjusting a few > numbers > so that you can either index the new virtual slice with an integer and return > the > element, in which case the index into the original tuple will be > someoffset+i*somefactor once you get past the limit checks for the virtual > slice. By the same token, transforming a few numbers of one virtual slice > into similar numbers for a a new virtual slice of that shouldn't be rocket > science. > And it wouldn't have to be done more than once. Don't have time to do it now, > but there are plenty around here that could, I'm sure. > > Regards, > Bengt Richter
Here's my (undocumented) version of it: http://rafb.net/paste/results/HkxmHp37.html and its unit test: http://rafb.net/paste/results/2LIInT68.html And some useless timing comparisons (I know it's a stupid example, don't flame me for this): $ python /usr/lib/python2.3/timeit.py \ -s "x=tuple(xrange(10000))" \ "[x[1:-1] for n in xrange(100)]" 10 loops, best of 3: 3.84e+04 usec per loop $ python /usr/lib/python2.3/timeit.py \ -s "from immutableseq import ImmutableSequence" \ -s "x=ImmutableSequence(xrange(10000))" \ "[x[1:-1] for n in xrange(100)]" 100 loops, best of 3: 5.85e+03 usec per loop Feel free to comment or suggest improvements. George -- http://mail.python.org/mailman/listinfo/python-list
