On Tuesday, 24 March 2015 21:20:11 UTC-7, Chris Angelico wrote: > On Wed, Mar 25, 2015 at 3:04 PM, Paul Rubin <nobody> wrote: > > This works for me in Python 2.7 but I think > > Python 3 gratuitously broke tuple unpacking so it won't work there: > > > > ================================================================ > > > > from itertools import count, groupby > > old = [0, 0, 0, 1, 0, 0, 1, 0, 1, 1, 0, 1, 1, 1, 1, 0, 0, 0, 1, 1, 0, 1, 0, > > 1] > > new = [reduce(lambda x,(y,i):x*2+y, g, 0) > > for k,g in groupby(zip(old,count()), lambda (a,b): b//8)] > > print new > > > >>>> [18, 222, 53] > > ================================================================ > > You don't need tuple unpacking. Here's the Py3 version of the above: > > from functools import reduce > new = [reduce(lambda x,y:x*2+y[0], g, 0) > for k,g in groupby(zip(old,count()), lambda a: a[1]//8)] > > ChrisA
Now I have just read the latest spec and speed/memory may become issues: 1 bit images of a size of 1024 x 1280 need to be processed this way, so 1310720 list elements. Also needs to be 2.7 only. Any recommendations? -- https://mail.python.org/mailman/listinfo/python-list
