Revit, Dynamo, Pythonnode, create solids out of polycurves - but keep the structure of lists and sublists

this is the first Question I am asking around here. (Question is in the Header.) ` When I do this:

for curve in curves:

    for c in curve:
        Solid = c.ExtrudeAsSolid(direction, distance)

mylist1.append(mylist2)     `

the result is a List of Solids made out of all the polylines but not sorted in the original sublists. I get why it is like that..but can`t find the right solution. ^^ help?