print([[j[i] for j in l1] for i in range(len(l1[0])) ])
for j in l1] for i in range(len(l1[0]))
等价于
for i in range(len(L1[0])):
for j in L1:
j[i]
print([[j[i] for j in l1] for i in range(len(l1[0])) ])
for j in l1] for i in range(len(l1[0]))
等价于
for i in range(len(L1[0])):
for j in L1:
j[i]