Greg Ewing 在 2021年6月16日 星期三上午7:11:35 [UTC+8] 的信中寫道： > On 15/06/21 7:32 pm, Jach Feng wrote: > > But usually the list creation is not in simple way:-) for example: > >>>> a = [1,2] > >>>> m = [a for i in range(3)] > >>>> m > > [[1, 2], [1, 2], [1, 2]] > >>>> id(m[0]) == id(m[1]) == id(m[2]) > > True > The first line is only executed once, so you just get one > list object [1, 2]. You then refer to that object three times > when you build the outer list. > > To get three different [1, 2] lists you would need something > like this: > m = [[1,2] for i in range(3)] > This executes the [1, 2] expression 3 times. Because lists are > mutable, you can be sure that this will give you 3 distinct > list objects. > > -- > Greg Yes, I know. Here I just want to show another gutter I had found:-). Anyone else?
--Jach -- https://mail.python.org/mailman/listinfo/python-list
