Le 20/12/2020 à 21:00, danilob a écrit : > > > b = ((x[0] for x in a)) > There is a useless pair of parenthesis b = (x[0] for x in a) b is a GENERATOR expression first list(b) calls next method on b repetedly until b is empty. So it provides the "content" of b second list(b) provides nothing since b is empty (there is no reset on generators)