Le 06/04/17 à 14:25, Piet van Oostrum a écrit :
Steven D'Aprano <steve+comp.lang.pyt...@pearwood.info> writes: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...It is a poor man's 'let'. It would be nice if python had a real 'let' construction. Or for example: [(tmp, tmp + 1) for x in data with tmp = expensive_calculation(x)] Alas!
With two passes e = [expensive_calculation(x) for x in data] final = [(x, y+1) for x, y in zip(e, e)] Vincent -- https://mail.python.org/mailman/listinfo/python-list
