NumPy快速入门--复制/视图/深拷贝

>>> a = np.arange(12)
>>> b = a
>>> b is a
True
>>> b.shape
(12,)
>>> b.shape = 3,4
>>> a.shape
(3, 4)
>>> id(a)		#a、b的 id 号一样，没有创建新的数据
2432625948272
>>> id(b)
2432625948272

>>> def f(x):
	print(id(x))

	
>>> id(a)
2432625948272
>>> f(a)	# 传入函数的对象a的id打印出来和之前一样，没有新对象产生
2432625948272

>>> c = a.view()
>>> c is a
False
>>> c.base is a
True
>>> c.flags.owndata	# 返回 False，c 并不保管数据
False
>>> a.flags.owndata	# 返回 True，数据由 a 保管
True
>>> c.shape
(3, 4)
>>> a.shape
(3, 4)
>>> c.shape = 2,6	# 形状不会同步
>>> c[0,4] = 1234	# 共享数据，a的也会变，数据同步
>>> c
array([[   0,    1,    2,    3, 1234,    5],
       [   6,    7,    8,    9,   10,   11]])
>>> a
array([[   0,    1,    2,    3],
       [1234,    5,    6,    7],	 # 1234也在里面
       [   8,    9,   10,   11]])

>>> s = a[:,1:3]	# s是a的切片，是a的一个view
>>> s
array([[ 1,  2],
       [ 5,  6],
       [ 9, 10]])
>>> s[:] = 999		# s 全部改数据
>>> s
array([[999, 999],
       [999, 999],
       [999, 999]])
>>> a				# a中的s切片部分数据都被改了
array([[   0,  999,  999,    3],
       [1234,  999,  999,    7],
       [   8,  999,  999,   11]])

>>> a = np.arange(12).reshape(3,4)
>>> a
array([[ 0,  1,  2,  3],
       [ 4,  5,  6,  7],
       [ 8,  9, 10, 11]])
       
>>> d = a.copy()		# 新的对象
>>> d is a
False
>>> d.base is a			# 与a没有任何联系
False
>>> d[0,0] = 999
>>> d
array([[999,   1,   2,   3],
       [  4,   5,   6,   7],
       [  8,   9,  10,  11]])
>>> a
array([[ 0,  1,  2,  3],
       [ 4,  5,  6,  7],
       [ 8,  9, 10, 11]])