了解列表推导式（和嵌套LC）的语法

Question

这有效：

allDasTickets = ["9255955", "9255958", "9255960", "9255977"]
[[j for j in allDasTickets if x != j] for x in allDasTickets]

['9255958', '9255960', '9255977']
['9255955', '9255958', '9255977']
['9255958', '9255960', '9255977']
['9255955', '9255958', '9255960']

但这不是：

allDasTickets = ["9255955", "9255958", "9255960", "9255977"]
[for x in allDasTickets [j for j in allDasTickets if x != j]]
File "<stdin>", line 1
[for x in allDasTickets [j for j in allDasTickets if x != j]]
   ^

Answer 1

对于列表理解，语法为

[ <something> for elem in sequence]

<something>本身可以用作列表推导。同时，对于嵌套循环（但不是嵌套列表）的理解，语法为

[<something> for elem in outerseq for elem2 in innerseq]

以同样的方式，依此类推。