Nobody wrote: > On Tue, 20 Sep 2016 15:12:39 +0200, Peter Otten wrote: > >> because they don't build lists only to throw them away. > > The lists could have been avoided by using iterators, e.g. > > import itertools as it > keys = xrange(256) > vals = it.imap(chr, keys) > max(it.imap(operator.setitem, it.repeat(d), keys, vals)) > >> Also, creating a list of dicts or lists is a common gotcha because after >> >> outer = [[]] * 3 >> >> the outer list contains *the* *same* list three times, not three empty >> lists. > > But in this case, it's not a gotcha;
Remember that the OP is a newbie > it's intentional and the author of the original example is trying to be clever, but in my eyes doesn't succeed. > that each iteration > operates upon the same dictionary. > > Essentially, [d]*len(keys) is a trick to get around the fact that map() > requires all of the arguments (apart from the function) to be sequences. > > itertools.repeat() is possibly a better trick, although then you can't use > map(), because map() iterates until *all* sequences are exhausted, > appending None values for shorter sequences. itertools.imap() terminates > once the shortest sequence is exhausted. > > In this specific case, a loop or comprehension would have been better. But > in situations where you don't control the iteration, the ability to coerce > something into a pre-determined iteration pattern is useful. You mean there is a situation where you'd actually recommend/use > max(it.imap(operator.setitem, it.repeat(d), keys, vals)) ? I'd like to see that use case. On second thought -- we might both settle on "Recommended by nobody" ;) -- https://mail.python.org/mailman/listinfo/python-list
