TypeError: can't pickle ufunc objects

TypeError: can’t pickle ufunc objects

$ python - <<'PY'
import numpy as np
import pickle
pickle.dumps(np.add)
PY
# TypeError: can't pickle ufunc objects

Why this happens

NumPy ufuncs are C-level function pointers and are not picklable by default. The Python pickle module cannot serialize C-level functions like np.add, np.multiply, or other ufunc objects.

Fix

Avoid pickling ufuncs directly. Instead, pickle a string name or an enum describing the operation and map it back to a ufunc at load time. Alternatively, use dill or custom serialization for complex objects, or wrap the operation in a Python-level callable that can be pickled.

Wrong code

import numpy as np
import pickle
# Trying to pickle a ufunc directly
pickle.dumps(np.add)

Fixed code

import numpy as np
import pickle
# Serialize a reference to the function by name
pickled = pickle.dumps('add')
name = pickle.loads(pickled)
ufunc = getattr(np, name)
print(ufunc(1, 2))  # 3

# Or use Python wrapper that is picklable
def add(x, y):
    return np.add(x, y)
print(pickle.dumps(add))