Demonstrates how to use scripting to modify and existing part.
*Edit line 4 in the script to reflect your directory path and part name.
# demonstrates opening an existing part and adding a 3d sketch to it
# load P:\work\TestPart.AD_PRT
MyPart = Part(r'C:\Users\<username>\Desktop\ScriptDir', 'New')
# create a 3D sketch
Route = MyPart.Add3DSketch('Route')
Route.AddBspline([0, 0, 0, 5, 0, 0, 10, 5, 5, 15, 10, 5, 15, 15, 15])