不可变的数字阵列?

有没有一种简单的方法来创建一个不可变的 NumPy 数组?

如果必须从 ndarray派生一个类才能做到这一点,那么为了实现不可变性必须重写的最小方法集是什么?

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You can make a numpy array unwriteable:

a = np.arange(10)
a.flags.writeable = False
a[0] = 1
# Gives: ValueError: assignment destination is read-only

Also see the discussion in this thread:

http://mail.scipy.org/pipermail/numpy-discussion/2008-December/039274.html

and the documentation:

http://docs.scipy.org/doc/numpy/reference/generated/numpy.ndarray.flags.html

I have a subclass of Array at this gist: https://gist.github.com/sfaleron/9791418d7023a9985bb803170c5d93d8

It makes a copy of its argument and marks that as read-only, so you should only be able to shoot yourself in the foot if you are very deliberate about it. My immediate need was for it to be hashable, so I could use them in sets, so that works too. It isn't a lot of code, but about 70% of the lines are for testing, so I won't post it directly.

Note that it's not a drop-in replacement; it won't accept any keyword args like a normal Array constructor. Instances will behave like Arrays, though.

Setting the flag directly didn't work for me, but using ndarray.setflags did work:

a = np.arange(10)
a.setflags(write=False)
a[0] = 1  # ValueError