RuntimeError: output array is read-only

output array is read-only

$ python - <<'PY'
import numpy as np
data = np.arange(4)
view = data.view()
view.setflags(write=False)
np.add(data, 1, out=view)
PY
Traceback (most recent call last):
  File "<stdin>", line 6, in <module>
RuntimeError: output array is read-only

Why this happens

You passed an array flagged as non-writeable (or a view of a read-only buffer) as the destination for an operation using out=. NumPy prevents in-place writes to protect memory safety.

Fix

Ensure the destination array is writeable (remove read-only flag or copy the array) or avoid using out= and assign the result to a new array.

Wrong code

import numpy as np
data = np.arange(4)
view = data.view()
view.setflags(write=False)
np.add(data, 1, out=view)

Fixed code

import numpy as np
data = np.arange(4)
view = data.view()
# make a copy or set flags if appropriate
copy = view.copy()
np.add(data, 1, out=copy)

# or make writeable (only if you control ownership)
# view.setflags(write=True)