Op 09-01-17 om 04:53 schreef Steven D'Aprano: > Suppose you have an expensive calculation that gets used two or more times in > a > loop. The obvious way to avoid calculating it twice in an ordinary loop is > with > a temporary variable: > > result = [] > for x in data: > tmp = expensive_calculation(x) > result.append((tmp, tmp+1)) > > > But what if you are using a list comprehension? Alas, list comps don't let > you > have temporary variables, so you have to write this: > > > [(expensive_calculation(x), expensive_calculation(x) + 1) for x in data] > > > Or do you? ... no, you don't! > > > [(tmp, tmp + 1) for x in data for tmp in [expensive_calculation(x)]] > > > I can't decide whether that's an awesome trick or a horrible hack...
Maybe this in an occasion to use your recipe. http://code.activestate.com/recipes/580625-collection-pipeline-in-python/ result = data | Map(expensive_calculation) | Map(lambda tmp: (tmp, tmp + 1)) | List -- Antoon. -- https://mail.python.org/mailman/listinfo/python-list
