Describe the issue:

Hi,
At PyVista, we test against thenumpy nightly wheels. Our tests recently failed and a patch (pyvista/pyvista#7538) was needed to fix the tests. However, I think this patch should not be needed, and is in fact a regression withnumpy (i.e. a bug has been introduced).

I locally checked out, installed, and tested against recent commits to main and found that the regression is caused by#29006

As mentioned inpyvista/pyvista#7538, our tests usually pass with

assertnp.array_equal([42], [42])

But with#29006, we are getting variable results like:

assertnp.array_equal([1], [42])

assertnp.array_equal([44636345150720], [42])

I don't really understand the changes in#29006 or how they might cause this, but from our end the error is generated for a special case where our code creates a temporary object internally to store the array, and it seems the reference to the array is being lost somehow or pre-maturely freed, causing the array values to be corrupted.

The code below fails with commit0506cf6, but succeeds withc2d5e00 (i.e. the commit immediately preceding). I tried creating a minimal example using onlynumpy, but the references to the array are complex and difficult to reproduce since PyVista wraps a lower-level C++ package (VTK) which also holds its own references to the array data.

Reproduce the code example:

importpyvistaaspvimportnumpyasnp# Define an array-like inputkey='data'value= [42]# Store the array with a container# internally, the array is cast as an `ndarray` instancemulti=pv.MultiBlock()multi.field_data[key]=value# Nest the container into anothername='nested'root=pv.MultiBlock({name:multi})# Move the array from the nested container to the root.# Internally, this method will use a temp object to store the arrayseparator='::'root.move_nested_field_data_to_root(field_data_mode='prepend',separator=separator)# The root container should now contain the values from the nested# array that was moved to the rootnew_key=name+separator+keyassertnp.array_equal(root.field_data[new_key],value)# ERROR

Error message:

N/A

Python and NumPy Versions:

2.3.0.dev0+git20250519.0506cf6
3.12.2 (v3.12.2:6abddd9f6a, Feb 6 2024, 17:02:06) [Clang 13.0.0 (clang-1300.0.29.30)]

Runtime Environment:

No response

Context for the issue:

This bug seems to cause arrays to be pre-maturely gc'd in some cases, which should probably be avoided. And the root cause has been identified, meaning that the fix can be easily implemented with a simple revert.