RuntimeWarning: invalid value encountered in <ufunc>

7 Dec 2025

1 min read

RuntimeWarning: invalid value encountered

$ python -c "import numpy as np; np.log(np.array([-1.0]))"
/tmp/...: RuntimeWarning: invalid value encountered in log
  np.log(np.array([-1.0]))

Why this happens

The operation produced an undefined result (NaN or complex), but NumPy continues and emits a RuntimeWarning instead of raising.

Fix

Validate inputs or use complex dtypes if complex results are expected. Handle NaNs after the operation.

Wrong code

import numpy as np
print(np.log(np.array([-1.0, 2.0])))

Fixed code

import numpy as np
arr = np.array([-1.0, 2.0])
res = np.empty_like(arr)
mask = arr > 0
res[mask] = np.log(arr[mask])
res[~mask] = np.nan
print(res)

# or use complex dtype
print(np.log(arr.astype(np.complex128)))