Gr_modtool error

Hi everyone,

I urgently need to write a new block in GNURadio. I am newbie so at
first I want to do exaple block.

But unfortunately gr_modtool says:

carter@inspiron:~/sdr/gr-howto$ add -t general square_ff
Traceback (most recent call last):
File “/bin/”, line 460, in
class GRMTemplate(Cheetah.Template.Template):
NameError: name ‘Cheetah’ is not defined

It’s very weir because before I reinstalled my linux, gr_modtool was
working fine.