OFDM Modification

Hi,

I use an array to implement supporting multi-constellation scheme for
OFDM system, but
I got a problem in modifying the code for /trunk/
gnuradio-core/src/python/gnuradio/blks2impl/ofdm.py

in which I generate a parameter multi_modulation[i][j]
while i is the ith subcarrier, and j is the used modulation scheme.
However, I have no idea how to modify the following :

 expert.add_option("","--multi_modulation",type ="array", default = 

“”,
help=“set the number of use multi_constellation decision
[defalut=%default]”)

where I want to use “bpsk” as default for whole subcarrier, and type
array to assign which subcarrier should use other constellation scheme.
For example [2 “qpks” ; 5 “16qam”] means the 2nd subcarrier use qpsk,
and the 5th subcarrier use 16qam.

Another question is, what’s the meaning for the parameter arity? I
thought I also need to change it to an array for different subcarriers,
but I also got stuck there.