A discussion [1] is currently underway at GitHub which will benefit from a larger forum. In version 1.9, the diagonal() method was changed to return a read-only (non-contiguous) view into the original array instead of a plain copy. Also, it has been announced [2] that in 1.10 the view will become read/write. A concern has now been raised [3] that this change breaks backward compatibility too much. Consider the following code: x = numy.eye(2) d = x.diagonal() d[0] = 2 In 1.8, this code runs without errors and results in [2, 1] stored in array d. In 1.9, this is an error. With the current plan, in 1.10 this will become valid again, but the result will be different: x[0,0] will be 2 while it is 1 in 1.8. Two alternatives are suggested for discussion: 1. Add copy=True flag to diagonal() method. 2. Roll back 1.9 change to diagonal() and introduce an additional diagonal_view() method to return a view. [1] https://github.com/numpy/numpy/pull/5409 [2] http://docs.scipy.org/doc/numpy/reference/generated/numpy.diagonal.html [3] http://khinsen.wordpress.com/2014/09/12/the-state-of-numpy/