NumPy has the efficient function/method
nonzero() to identify the indices of non-zero elements in an
ndarray object. What is the most efficient way to obtain the indices of the elements that do have a value of zero?
numpy.where() is my favorite.
>>> x = numpy.array([1,0,2,0,3,0,4,5,6,7,8]) >>> numpy.where(x == 0) array([1, 3, 5])