Does assignment with advanced indexing copy array data?

Question

I am slowly trying to understand the difference between views and copys in numpy, as well as mutable vs. immutable types.

If I access part

Answer 1

Yes, it is the same object. Here's how you check:

>>> a
array([[ 0.,  0.,  0.],
       [ 0.,  0.,  0.],
       [ 0.,  0.,  0.]])
>>> a2 = a
>>> a[b] = 1
>>> a2 is a
True
>>> a2
array([[ 1.,  0.,  0.],
       [ 0.,  1.,  0.],
       [ 0.,  0.,  1.]])

Assigning to some expression in Python is not the same as just reading the value of that expression. When you do c = a[b], with a[b] on the right of the equals sign, it returns a new object. When you do a[b] = 1, with a[b] on the left of the equals sign, it modifies the original object.

In fact, an expression like a[b] = 1 cannot change what name a is bound to. The code that handles obj[index] = value only gets to know the object obj, not what name was used to refer to that object, so it can't change what that name refers to.