Setting ras3 in Psithon

I’m trying to run some RAS calculations where all orbitals are correlated.

Unfortunately, this appears to require setting RAS1, RAS2 and RAS3 in detci. The size of RAS3 is determined by the number of virtual orbitals, which, however, may be geometry specific. So I’d like to set it Psithon side as

nras3 = wf.nocc()-nact
set ras3 [ nras3 ]

but this appears to not work - in the output ras3=0. What’s the proper way to do this?