f=lambda l:sum([[x[::-1],x][i&1]for i,x in enumerate(l)],[])
print(f([[4, 3, 2, 1], [5, 6, 7, 8], [12, 11, 10, 9], [13, 14, 15, 16]]))
Zj1sYW1iZGEgbDpzdW0oW1t4Wzo6LTFdLHhdW2kmMV1mb3IgaSx4IGluIGVudW1lcmF0ZShsKV0sW10pCnByaW50KGYoW1s0LCAzLCAyLCAxXSwgWzUsIDYsIDcsIDhdLCBbMTIsIDExLCAxMCwgOV0sIFsxMywgMTQsIDE1LCAxNl1dKSk=
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]