Problem with the OOT forecast() method in Python

Hello GNURadio Community, 

I am getting a TypeError when I fill in the code in the forecast() method in my Gnuradio OOT block design. I know, if I want to interpolate or decimate, I can simply pick the block type in the gr_modtool design menu, however, I would like to develop the capability to design my own. Here is how I fill in the forecast() method in Python to do either decimation or interpolation:

ninput_items_required[0] = noutput_items*self.sps  # for decimation

OR

ninput_items_required[0] = noutput_items/self.sps  # for interpolation

On running the flowgraph in GRC Console I see TypeError: 'int' object does not support item assignment.

Will appreciate any suggestion to fix this problem.

George