python 二维数组 行列转换

arr = [[1,2,3,4],[5,6,7,8],[9,10,11,12]]

#方法1
ar2 =[]
for i in range(len(arr[0])):
b =[]
for j in range(len(arr)):
b.append(arr[j][i])
ar2.append(b)
print(ar2)

#方法2
ar2 = list(map(list,zip(*arr)))
print(ar2)

#方法3
ar2 = [ [row[i] for row in arr] for i in range(len(arr[0])) ]
print(ar2)