X -= X[::, None]
which is also equivalent to
X -= X[::, np.newaxis]
So slice(None) is adding "::", and the None as the last element in tup is adding a new axis.
It is like placehoder.
same as df[col]=None in Pandas to generate a new column.
Written by Ke Gui
An ordinary guy who wants to be the reason someone believes in the goodness of people. He is living at Brisbane, Australia, with a lovely backyard.