Improving the error message when adding i8 array to u8 array

When attempting to add an ndarray of type int64 to an ndarray of type uint64, numpy throws a TypeError:

TypeError: Cannot cast ufunc add output from dtype('float64') to dtype('uint64') with casting rule 'same_kind'

The error message incorrectly identifies the type of the first array as float64, when it is actually int64.

Reproducing code example:

import numpy as np
x = np.arange(5, dtype='u8')
y = np.arange(5, dtype='i8')
x += y

Error message:

TypeError: Cannot cast ufunc add output from dtype('float64') to dtype('uint64') with casting rule 'same_kind'

Numpy/Python version information:

Tested with Python 3:

1.16.4 3.6.8 (default, Oct  7 2019, 12:59:55) 
[GCC 8.3.0]

Also with Python 2:

('1.15.1', '2.7.15+ (default, Oct  7 2019, 17:39:04) \n[GCC 7.4.0]')

[eric-wieser]

Let’s wait and see if any progress is made on #14843

[mattip]

Hi @5aumy4, welcome. As with many of these issues, it turns out to be more difficult than a simple error message change. See gh-14843.

As for getting started, you can read our contribution guide