how to do differential form in sympy

[chaowen guo]

HI:

I want to do differential form in sympy just like that in sagemath (http://doc.sagemath.org/html/en/reference/tensor/sage/tensor/differential_form_element.html)

Then I google sympy differential form, and find class sympy.diffgeom.Differential(form_field) in http://docs.sympy.org/latest/modules/diffgeom.html

However, if I try:

from sympy.diffgeom.rn import R2
from sympy.diffgeom import Differential
from sympy.diffgeom import WedgeProduct
import sympy
s_field=sympy.sin(R2.x*R2.y)
Differential(s_field)

it just output d(sin(xy)) but not expand to any one form just like:

y*cos(x*y)*dx + x*cos(x*y)*dy

I try to use expand but still not working.

So I want to ask whether sympy.diffgeom can do the job. If it can, how to write the source code? If it can not, is there other module in sympy can do the job?