numpy 的索引

import numpy as np

arr1 = np.arange(2,14)
print(arr1)
print(arr1[2:5])
print(arr1[2:-1])
print(arr1[:5])
arr2 =  arr1.reshape(3,4)
print(arr2)
print(arr2[1]) #取出第一行
print(arr2[1][1] , arr2[2,1]) # 取出第一行第1列的元素 ..
print(arr2[:,2]) #取出第二列
for i in arr2.T:
    print(i)
for i in arr2.flat: # 一个元素的迭代
    print(i,end=' ')