Take this code:
import itertools as it
import numpy as np
data = ['a','b','c','d']
dw = np.array([1, 3], dtype=np.int64)
print(list(it.islice(data,dw[0],dw[1],1)))
On Python 2.7 it prints ['b', 'c',] as expected.
On Python 3.6 it throws an exception:
ValueError: Stop argument for islice() must be None or an integer: 0 <= x <= sys.maxsize.
The same goes for np.int32, and other methods of the itertools package throw similar errors, e.g. when you use permutations you get TypeError: Expected int as r.
I couldn't find much on this apart from this numpy issue and related ones, but that one was closed 3 years ago implying it was solved.
And basic things like indexing with numpy ints data[dw[0]] or boolean comparisons like dw[0] == 1 work just fine.
Am I missing something? Could this be a Python 3 bug?