# SageMath code for working with modular form 882.2.f.b


# Compute space of new eigenforms: 
from sage.modular.dirichlet import DirichletCharacter
H = DirichletGroup(882, base_ring=CyclotomicField(6))
chi = DirichletCharacter(H, H._module([4, 0]))
N = Newforms(chi, 2, names="a") 

# select newform: 
traces = [2,-1,0,-1,-1,-3,0,2,-6]
f = next(g for g in N if [g.coefficient(i+1).trace() for i in range(9)] == traces)

# q-expansion: 
f.q_expansion() # note that sage often uses an isomorphic number field