Numpy: Should I use newaxis or None?
Solution 1:
None is allowed because numpy.newaxis is merely an alias for None.
In [1]: import numpy
In [2]: numpy.newaxis is None
Out[2]: True
The authors probably chose it because they needed a convenient constant, and None was available.
As for why you should prefer newaxis over None: mainly it's because it's more explicit, and partly because someday the numpy authors might change it to something other than None. (They're not planning to, and probably won't, but there's no good reason to prefer None.)