How to Fix FutureWarning: elementwise comparison failed; returning scalar, but in the future will perform elementwise comparison

To fix the FutureWarning: elementwise comparison failed; returning scalar, but in the future will perform elementwise comparison, you can use the .astype() function to ensure that both arrays have the same data type before comparing.

Python raises FutureWarning: elementwise comparison failed; returning scalar, but in the future will perform elementwise comparison when you are attempting to compare two NumPy arrays with different data types.

Reproducing the warning

import numpy as np

np.arange(3) == np.arange(3).astype(str)

Output

FutureWarning: elementwise comparison failed; returning scalar instead, 
               but in the future will perform elementwise comparison

You can see that the warning you’re encountering is caused by attempting to compare two NumPy arrays with different data types. The first array (np.arange(3)) contains integers, while the second array (np.arange(3).astype(str)) has been cast to strings.

How to fix it

You can either convert the first array to a string or the second array to an integer, depending on your use case.

Here are examples of both approaches.

Convert the first array to a string

You can convert a numpy array’s data type using the .astype() function.

import numpy as np

string_arr = np.arange(3).astype(str)
result = string_arr == np.arange(3).astype(str)

If you run the above code, you will not get any error because both arrays have an integer data type.

Convert the second array to an integer

import numpy as np

integer_array = np.arange(3)
result = integer_array == np.arange(3).astype(int)

In either case, the comparison will now be performed elementwise without raising a warning.

That’s it.