How to operate elementwise on a matrix of type scipy.sparse.csr_matrix?

Question

In numpy if you want to calculate the sinus of each entry of a matrix (elementise) then

a = numpy.arange(0,27,3).reshape(3,3)
numpy.sin(a)

will get the job done! If you want the power let's say to 2 of each entry

a**2

will do it.

But if you have a sparse matrix things seem more difficult. At least I haven't figured a way to do that besides iterating over each entry of a lil_matrix format and operate on it.

I've found this question on SO and tried to adapt this answer but I was not succesful.

The Goal is to calculate elementwise the squareroot (or the power to 1/2) of a scipy.sparse matrix of CSR format.

What would you suggest?