swev-id: astropy__astropy-14995 Fix NDDataRef mask propagation when other operand has no mask

[casey-brooks]

Issue

• Closes NDDataRef mask propagation fails in v5.3 when operand has no mask (bitwise_or) #82

Reproduction

1. In a clean checkout of astropy__astropy-14995, launch Python and run

   import numpy as np
   from astropy.nddata import NDDataRef
   
   mask = np.array([[True, False], [False, True]])
   data = np.array([[1, 2], [3, 4]])
   NDDataRef(data=data, mask=mask).multiply(1.0, handle_mask=np.bitwise_or)

2. Swap operand order to exercise commutativity:

   import numpy as np
   from astropy.nddata import NDDataRef
   
   mask = np.array([[True, False], [False, True]])
   data = np.array([[1, 2], [3, 4]])
   masked = NDDataRef(data=data, mask=mask)
   unmasked = NDDataRef(data=data)
   masked.multiply(unmasked, handle_mask=np.bitwise_or)

Observed failure

Scalar operand with np.bitwise_or

/workspace/astropy/astropy/version.py:12: UserWarning: could not determine astropy package version; this indicates a broken installation
  warnings.warn(
Traceback (most recent call last):
  File "<stdin>", line 6, in <module>
  File "/workspace/astropy/astropy/nddata/mixins/ndarithmetic.py", line 618, in multiply
    return self._prepare_then_do_arithmetic(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/workspace/astropy/astropy/nddata/mixins/ndarithmetic.py", line 731, in _prepare_then_do_arithmetic
    result, init_kwds = operand._arithmetic(operation, operand2, **kwargs)
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/workspace/astropy/astropy/nddata/mixins/ndarithmetic.py", line 335, in _arithmetic
    kwargs["mask"] = self._arithmetic_mask(
                     ^^^^^^^^^^^^^^^^^^^^^^
  File "/workspace/astropy/astropy/nddata/mixins/ndarithmetic.py", line 527, in _arithmetic_mask
    return handle_mask(self.mask, operand.mask, **kwds)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: unsupported operand type(s) for |: 'bool' and 'NoneType'

NDDataRef commutativity with np.bitwise_or

/workspace/astropy/astropy/version.py:12: UserWarning: could not determine astropy package version; this indicates a broken installation
  warnings.warn(
Traceback (most recent call last):
  File "<stdin>", line 7, in <module>
  File "/workspace/astropy/astropy/nddata/mixins/ndarithmetic.py", line 618, in multiply
    return self._prepare_then_do_arithmetic(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/workspace/astropy/astropy/nddata/mixins/ndarithmetic.py", line 734, in _prepare_then_do_arithmetic
    result, init_kwds = cls._arithmetic(
                        ^^^^^^^^^^^^^^^^
  File "/workspace/astropy/astropy/nddata/mixins/ndarithmetic.py", line 335, in _arithmetic
    kwargs["mask"] = self._arithmetic_mask(
                     ^^^^^^^^^^^^^^^^^^^^^^
  File "/workspace/astropy/astropy/nddata/mixins/ndarithmetic.py", line 527, in _arithmetic_mask
    return handle_mask(self.mask, operand.mask, **kwds)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: unsupported operand type(s) for |: 'bool' and 'NoneType'

Fix

• Guard _arithmetic_mask against operand is None and capture the operand's mask before accessing it.
• Return deep copies of whichever mask is present when the other operand lacks a mask so mask handlers never receive None inputs.
• Preserve the existing handler path for the both-masked case.

Tests

• Added regression tests covering scalar operands, NDDataRef commutativity, dual-mask combination, mask-less operands, and numpy array operands with both np.bitwise_or and np.logical_or handlers.
• pytest astropy/nddata/mixins/tests/test_ndarithmetic.py -q
• tox -e codestyle -- --files astropy/nddata/mixins/ndarithmetic.py astropy/nddata/mixins/tests/test_ndarithmetic.py

[casey-brooks]

Local Verification

• pytest astropy/nddata/mixins/tests/test_ndarithmetic.py -q → 189 passed
• tox -e codestyle -- --files astropy/nddata/mixins/ndarithmetic.py astropy/nddata/mixins/tests/test_ndarithmetic.py → passes

[noa-lucent]

Thanks for the thorough regression coverage. The arithmetic mask logic now copies whichever mask is present so we no longer hand None to custom mask handlers, and the new tests exercise both scalar and NDDataRef operands. I left one minor cleanup request inline.

[casey-brooks]

Test & Lint Summary

• SETUPTOOLS_USE_DISTUTILS=stdlib PYTHONPATH=. LD_LIBRARY_PATH=/nix/store/wffgswxkp55xi14jy63rjsnfvl2qvmxy-gcc-14.3.0-lib/lib:/nix/store/qipd93x9gjyiygqk673rd2ssnf8y7jj0-gcc-14.3.0-lib/lib:/nix/store/zmjqwzhgl9hwr8xnk8raj8d50lzkql66-gcc-14.3.0-lib/lib:/nix/store/n5lymg0y5x6i9wipkjrsi8aczv1nr4qc-zlib-1.3.1/lib${LD_LIBRARY_PATH:+:$LD_LIBRARY_PATH} .venv/bin/python -m pytest astropy/nddata/mixins/tests/test_ndarithmetic.py -q
  • result: 189 passed (UserWarning: could not determine astropy package version)
• SETUPTOOLS_USE_DISTUTILS=stdlib LD_LIBRARY_PATH=/nix/store/wffgswxkp55xi14jy63rjsnfvl2qvmxy-gcc-14.3.0-lib/lib:/nix/store/qipd93x9gjyiygqk673rd2ssnf8y7jj0-gcc-14.3.0-lib/lib:/nix/store/zmjqwzhgl9hwr8xnk8raj8d50lzkql66-gcc-14.3.0-lib/lib:/nix/store/n5lymg0y5x6i9wipkjrsi8aczv1nr4qc-zlib-1.3.1/lib${LD_LIBRARY_PATH:+:$LD_LIBRARY_PATH} .venv/bin/tox -e codestyle -- --files astropy/nddata/mixins/ndarithmetic.py astropy/nddata/mixins/tests/test_ndarithmetic.py
  • result: passed

[noa-lucent]

Thanks for the quick cleanup. The stray comment is gone and everything else still looks good. Approved.

[rowan-stein]

Approve: mask propagation fixes validated; tests and codestyle passed.