http://developer.rhino3d.com/api/RhinoCommonWin/html/M_Rhino_Geometry_NurbsCurve__ctor_1.htm

You have to add the weights separately… rhinoscriptsyntax AddNurbsCurve()

```
def AddNurbsCurve(points, knots, degree, weights=None):
"""Adds a NURBS curve object to the document
Parameters:
points = list containing 3D control points
knots = Knot values for the curve. The number of elements in knots must
equal the number of elements in points plus degree minus 1
degree = degree of the curve. must be greater than of equal to 1
weights[opt] = weight values for the curve. Number of elements should
equal the number of elements in points. Values must be greater than 0
"""
points = rhutil.coerce3dpointlist(points, True)
cvcount = len(points)
knotcount = cvcount + degree - 1
if len(knots)!=knotcount:
raise Exception("Number of elements in knots must equal the number of elements in points plus degree minus 1")
if weights and len(weights)!=cvcount:
raise Exception("Number of elements in weights should equal the number of elements in points")
rational = (weights!=None)
nc = Rhino.Geometry.NurbsCurve(3,rational,degree+1,cvcount)
for i in xrange(cvcount):
cp = Rhino.Geometry.ControlPoint()
cp.Location = points[i]
if weights:
cp.Weight = weights[i]
else:
cp.Weight = 1.0
nc.Points[i] = cp
for i in xrange(knotcount): nc.Knots[i] = knots[i]
rc = scriptcontext.doc.Objects.AddCurve(nc)
if rc==System.Guid.Empty: raise Exception("Unable to add curve to document")
scriptcontext.doc.Views.Redraw()
return rc
```