This is because slicing with a boolean has just no confusing meaning I
can think of [1]. NumPy even used to reject it, but there seems no
reason to add maintenance/code complexity (i.e. duplicate code from
Python already provides) to reject bools. There used to be a reason to
using `__index__()` i
I noticed that np.bool_.__index__() gives a DeprecationWarning
>>> np.bool_(True).__index__()
__main__:1: DeprecationWarning: In future, it will be an error for
'np.bool_' scalars to be interpreted as an index
1
This is good, because booleans don't actually act like integers in
indexing contexts.
