import vcsn c = vcsn.context('lal_char, q')
e = c.expression('<2>a(b+<3>c)') x = e.expansion() x
x.lweight(w), you may write
w * x.
c.weight('4') * x
You may even run the simpler:
4 * x
The expansion of a scalar product is the scalar product of the expansion: