列表推导式

 

 

matrix = [[1,2,3,4],[5,6,7,8],[9,10,11,12]]
list_row = [row[0] for row in matrix]
print(list_row)#[1, 5, 9]
list = [[row[i] for row in matrix] for i in range(4)]
print(list)#[[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]
print('for循环')
for i in range(4):
    for row in matrix:
        print(row[i])#1 5 9 2 6 10 3 7 11 4 8 12
lst = [row[i] for i in range(4) for row in matrix]
print(lst)#[1, 5, 9, 2, 6, 10, 3, 7, 11, 4, 8, 12]
print([x*y for x in range(1,5) if x>2 for y in range(1,4) if y<3])
for x in range(1,5):
    if x>2:
        for y in range(1,4):
            if y<3:
                print('x*y:',x*y)