DeprecationWarning: elementwise comparison failed

elementwise comparison failed

$ python - <<'PY'
import numpy as np
arr = np.array([1,2,3])
if arr == [1,2,3]:
    print('equal')
PY
DeprecationWarning: elementwise comparison failed; this will raise in a future version of numpy."

Why this happens

Comparing arrays to scalars or lists may trigger elementwise comparisons that produce arrays of booleans. Using that result in a context expecting a single boolean is ambiguous. In some cases comparisons with incompatible types fall back to object-level comparisons and raise warnings.

Fix

Use np.array_equal, np.allclose, arr.tolist() or explicit elementwise checks depending on whether you need exact equality or approximate.

Wrong code

import numpy as np
arr = np.array([1,2,3])
if arr == [1,2,3]:
    print('equal')

Fixed code

import numpy as np
arr = np.array([1,2,3])
if np.array_equal(arr, [1,2,3]):
    print('exactly equal')

# or for floats
if np.allclose(arr.astype(float), [1.,2.,3.]):
    print('approximately equal')