Numpy: Should I use newaxis or None?

Question

In numpy one can use the \'newaxis\' object in the slicing syntax to create an axis of length one, e.g.:

import numpy as np
print np.zeros((3,5))[:,np.newaxi         


        

Answer 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.)