I ran into the same problem. I needed a file with the extension .gsf for importing the flopy model to gms. I wrote the following code:
g=Gridgen(dis,exe_name='gridgen_x64', model_ws=gridgen_dir)
ncells = g.get_nodes()
verts, iverts = g.get_verts_iverts(ncells)
# vertices=g.get_vertices(ncells)
vertices = g.get_gridprops_vertexgrid()
lenverts=len(verts)
f = open("test.gsf", "a")
f.write('UNSTRUCTURED\n' + str(g.get_nodes()) + ' ' + str(g.get_nlay()) + ' ' +
str(1) + ' ' + str(1) + '\n' + str(
lenverts * (nlay+1)) + '\n')
tuples = []
count = 0
for i in g.get_top():
if count != ncells:
for j in g._vertdict[count]:
# np.savetxt(f, (j+(i,),), delimiter=' ', fmt='%g')
tuples.append(j + (i,))
count += 1
count=ncells-ncells/nlay
for i in list(g.get_bot()[int(ncells-ncells/nlay):int(ncells)]):
for j in g._vertdict[count]:
tuples.append(j + (i,))
count += 1
nvertexes = list(dict.fromkeys(tuples))
for i in range(0, ncells):
iverts[i] = [x + 1 for x in iverts[i]]
del iverts[i][-1]
for i in nvertexes:
np.savetxt(f, (i,), delimiter=' ', fmt='%g')
nodesgfs = []
nodeiter=0
for j in range(0,nlay):
for i in g.get_nod_recarray()[nodeiter:]:
ivertex=[x + lenverts*(j) for x in iverts[nodeiter]]
nodesgfs.append((i[0] + 1,) + (i[2],) + (i[3],) + (i[4],) + (i[1] + 1,)
+ (len(ivertex)*2,) + tuple([x + lenverts*(j+1) for x in
iverts[nodeiter]])+tuple(ivertex))
nodeiter += 1
if nodeiter in [numcell for numcell in range(int(ncells/nlay),ncells,int(ncells/nlay))]:
break
nodesgfs = list(dict.fromkeys(nodesgfs))
for i in nodesgfs:
np.savetxt(f, (i,), delimiter=' ', fmt='%g')