Blender 2.5x Python Curve from a List of Coordinates.

Given a list of coordinates in the form of Vector((x,y,z)) it is possible to string them together to get a curve shape. Each Point on a curve is has 4 values (x,y,z,w). W=weight and is a value between 0.010 and 100.

It took me a while to get some intuition in this part of blender bpy. This post is my effort to clear it up for myself and hopefully for others who may struggle with it in the future.

import bpy
from mathutils import Vector

w = 1 # weight
cList = [Vector((0,0,0)),Vector((1,0,0)),Vector((2,0,0)),Vector((2,3,0)),
        Vector((0,2,1))]

curvedata = bpy.data.curves.new(name='Curve', type='CURVE')
curvedata.dimensions = '3D'

objectdata = bpy.data.objects.new("ObjCurve", curvedata)
objectdata.location = (0,0,0) #object origin
bpy.context.scene.objects.link(objectdata)

polyline = curvedata.splines.new('POLY')
polyline.points.add(len(cList)-1)
for num in range(len(cList)):
    x, y, z = cList[num]
    polyline.points[num].co = (x, y, z, w)

or a slightly modified version, for turning it into a reusable function

import bpy
from mathutils import Vector

w = 1 # weight
listOfVectors = [Vector((0,0,0)),Vector((1,0,0)),Vector((2,0,0)),Vector((2,3,0)),
        Vector((0,2,1))]

def MakePolyLine(objname, curvename, cList):
    curvedata = bpy.data.curves.new(name=curvename, type='CURVE')
    curvedata.dimensions = '3D'

    objectdata = bpy.data.objects.new(objname, curvedata)
    objectdata.location = (0,0,0) #object origin
    bpy.context.scene.objects.link(objectdata)

    polyline = curvedata.splines.new('POLY')
    polyline.points.add(len(cList)-1)
    for num in range(len(cList)):
        x, y, z = cList[num]
        polyline.points[num].co = (x, y, z, w)

MakePolyLine("NameOfMyCurveObject", "NameOfMyCurve", listOfVectors)

If the list of vectors has only one Vector, then the curve will use one predefined zero vector (Vector((0,0,0))) and draw a straight line from 0,0,0 to your single Vector. Go into edit mode to see where the points are placed.

Each object can have multiple curves associated with it, they are accessed like this

# returns the number of curves associated with this object
>>> len(bpy.context.active_object.data.splines)

# returns the curve information associated with the first spline (index = 0) 
>>> bpy.context.active_object.data.splines[0]
bpy.data.curves["NameOfMyCurve"].splines[0]

# this returns the coordinates on that curve as a list.
>>> [point.co for point in bpy.context.active_object.data.splines[0].points]

if you want a smooth curve from these points, declare at the time of creation what type from these options ('POLY', 'BEZIER', 'BSPLINE', 'CARDINAL', 'NURBS')

import bpy  
from mathutils import Vector  
  
w = 1 # weight  
listOfVectors = [Vector((0,0,0)),Vector((1,0,0)),Vector((2,0,0)),Vector((2,3,0)),  
        Vector((0,2,1))]  
  
def MakePolyLine(objname, curvename, cList):  
    curvedata = bpy.data.curves.new(name=curvename, type='CURVE')  
    curvedata.dimensions = '3D'  
  
    objectdata = bpy.data.objects.new(objname, curvedata)  
    objectdata.location = (0,0,0) #object origin  
    bpy.context.scene.objects.link(objectdata)  
  
    polyline = curvedata.splines.new('NURBS')  
    polyline.points.add(len(cList)-1)  
    for num in range(len(cList)):  
        x, y, z = cList[num]  
        polyline.points[num].co = (x, y, z, w)  
  
    polyline.order_u = len(polyline.points)-1
    polyline.use_endpoint_u = True
    
  
MakePolyLine("NameOfMyCurveObject", "NameOfMyCurve", listOfVectors)

And here a more stripped down version

import bpy  
from mathutils import Vector  

# weight  
w = 1 

# we don't have to use the Vector() notation.  
listOfVectors = [(0,0,0),(1,0,0),(2,0,0),(2,3,0),(0,2,1)]  
  
def MakePolyLine(objname, curvename, cList):  
    curvedata = bpy.data.curves.new(name=curvename, type='CURVE')  
    curvedata.dimensions = '3D'  
  
    objectdata = bpy.data.objects.new(objname, curvedata)  
    objectdata.location = (0,0,0) #object origin  
    bpy.context.scene.objects.link(objectdata)  
  
    polyline = curvedata.splines.new('NURBS')  
    polyline.points.add(len(cList)-1)  
    for num in range(len(cList)):  
        polyline.points[num].co = (cList[num])+(w,)  
  
    polyline.order_u = len(polyline.points)-1
    polyline.use_endpoint_u = True
    
  
MakePolyLine("NameOfMyCurveObject", "NameOfMyCurve", listOfVectors)