The fact that `isinstance(np.float64(1), float)` raises the problem that the current implementation of np.float64 scalars breaks the Liskov substitution principle: `sequence_or_array[round(x)]` works if `x` is a float, but breaks down if x is a np.float64. See https://github.com/numpy/numpy/issues/11810, where the issue is discussed in the broader setting of the semantics of `np.round` vs. python3 `round`. I do not have a strong opinion here, except that if np.float64’s are within the python number hierarchy they should be PEP 3141 compliant (which currently they are not.) Stefano

On 25 Feb 2020, at 00:03, numpy-discussion-request@python.org wrote:

Also, something to think about is that currently numpy scalars satisfy the property `isinstance(np.float64(1), float)`, i.e they are within the python numerical type hierarchy. 0d arrays do not have this property. My proposal above would break this. I'm not sure what to think about whether this is a good property to maintain or not.

Cheers, Allan