ValueError: invalid pad mode for np.pad

ValueError: invalid pad mode for np.pad

$ python - <<'PY'
import numpy as np
arr = np.array([1, 2, 3])
np.pad(arr, 1, mode='mirror')
PY
# ValueError: mode 'mirror' is not understood

Why this happens

np.pad supports a fixed set of modes (e.g., 'constant', 'reflect', 'edge', 'symmetric'). Using an unsupported mode name (misspelling or an incorrect option) triggers a ValueError because NumPy cannot interpret how to pad the array.

Fix

Use a valid mode string or provide the appropriate pad_width and constant_values for 'constant' mode. Double-check the mode name spelling and consult np.pad docs for supported modes.

Wrong code

import numpy as np
arr = np.array([1, 2, 3])
np.pad(arr, 1, mode='mirror')  # 'mirror' is not a supported mode

Fixed code

import numpy as np
arr = np.array([1, 2, 3])
# Use a supported mode like 'reflect'
print(np.pad(arr, 1, mode='reflect'))
# Or use constant padding by setting mode='constant'
print(np.pad(arr, 2, mode='constant', constant_values=0))