How to change/set variables?

edit

I created a list of formal variables that I want to work with under addition, multiplication etc. in the following way:

g = list(var('g_%d' % i) for i in rang(4))

Specifically I'm working with differential forms

M = Manifold(4, 'M', field='complex')
U = M.open_subset('U')
c_xyXY<x, y, X, Y>=U.chart()
eU = c_xyXY.frame()
d = [[M.diff_form(2, name='d_{}{}'.format(j, i)) for i in range(2)] for j in range(2)]
d[0][0] [eU, 2, 0] = g[0]
d[0][1] [eU, 3, 0] = g[1]
d[1][0] [eU, 2, 1] = g[2]
d[1][1] [eU, 3, 1] = g[3]

I then want to set the variables to something specific like

g[0] = x^2

but when I try to display this I get

d[0][0].display(eU)
d_00 = -g_0dx/\dX

What I want is

d_00 = -x^2dx/\dX

EDIT: The question as originally asked has been sufficiently answered by eric_g below. However I'm still having difficulty with a more complicated version of the same set-up, which I present here: https://ask.sagemath.org/question/469...