Path following via API

Question

Apologies if this question has been answered already, but I can't seem to get this thing working.

What I am trying to do is have a cube follow a curve interpolated out of coordinates. Manually this would be done selecting both curve and cube and selecting "follow path" constraint in the Ctrl + P menu.

I have have put together a short script, but when I run it, the curve has the cube as a child, and there is a follow curve constraint. But the cube is not centered on the curve, and pressing play will not do anything.

I believe that I might be missing something conceptual, but can't really figure out what that is.

Thanks!

import bpy
Clearing scene
for item in bpy.data.objects:
    bpy.data.objects.remove(item)
Simulation Parameters
coords = [[0,0,0],[0,5,0],[0,0,15],[15,0,15], [0,0,20]]
bpy.ops.mesh.primitive_cube_add()
making curve
crv = bpy.data.curves.new('crv', 'CURVE')
crv.dimensions = '3D'
initialize spline
spline = crv.splines.new(type='NURBS')
a spline for each point
spline.points.add(len(coords)-1) # 1 point by default
assign the point coordinates to the spline points
for p, new_co in zip(spline.points, coords):
    p.co = (new_co + [1.0]) # (add nurbs weight)
make a new object with the curve
obj = bpy.data.objects.new('object_name', crv)
bpy.context.scene.collection.objects.link(obj)
obj.name = "Path"
Constraining Space craft to orbit
cube = bpy.context.scene.objects['Cube']
#cube.parent = bpy.context.scene.objects['Path'] 
bpy.ops.object.parent_set(type='FOLLOW')
cube.constraints.new('FOLLOW_PATH')  #Constraining cubesat to follow the path 
cube.constraints['Follow Path'].target=bpy.data.objects['Path']
cube.constraints["Follow Path"].forward_axis = 'FORWARD_X'
cube.constraints["Follow Path"].use_curve_follow = True
```

Answer 1

Some tweaks.

Took out the remove all objects, not a fan.

Use object references. After using an operator to add the cube

cube = context.object

after creating the curve obj it is known by reference as obj, no need to look it up as "Path".

When parenting via the operator, the selected objects are parented to the active. Have set the curve as active

context.view_layer.objects.active = obj

and selected the cube

cube.select_set(True)

before parenting via the operator.

Animate by setting an path duration (start to finish) in frames on the curve object, and keyframing or driving the evaluation time.

See Creating path curve using python script re using the end points of a nurbs curve

import bpy
context = bpy.context
Clearing scene
IMO never add this to a question script.
'''
for item in bpy.data.objects:
    bpy.data.objects.remove(item)
'''
Simulation Parameters
coords = [[0,0,0],[ 0,5,0], [0,0,15],[15,0,15], [0,0,20]]
bpy.ops.mesh.primitive_cube_add(location=coords[0])
cube = context.object
making curve
crv = bpy.data.curves.new('crv', 'CURVE')
crv.dimensions = '3D'
Animate the eval time (keyframes)
crv.path_duration = 250
crv.eval_time = 0
crv.keyframe_insert("eval_time", frame=1)
crv.eval_time = 10
crv.keyframe_insert("eval_time", frame=100)
crv.eval_time = 250
crv.keyframe_insert("eval_time", frame=250)
initialize spline
spline = crv.splines.new(type='NURBS')
spline.use_endpoint_u = True
spline.use_endpoint_v = True
a spline for each point
spline.points.add(len(coords)-1) # 1 point by default
assign the point coordinates to the spline points
for p, new_co in zip(spline.points, coords):
    p.co = (new_co + [1.0]) # (add nurbs weight)
make a new object with the curve
obj = bpy.data.objects.new('Path', crv)
context.scene.collection.objects.link(obj)
obj.select_set(True)
context.view_layer.objects.active = obj
cube.select_set(True)
#cube.parent = bpy.context.scene.objects['Path'] 
bpy.ops.object.parent_set(type='FOLLOW')
'''
cube.constraints.new('FOLLOW_PATH')  #Constraining cubesat to follow the path 
cube.constraints['Follow Path'].target = obj
cube.constraints["Follow Path"].forward_axis = 'FORWARD_X'
cube.constraints["Follow Path"].use_curve_follow = True
'''

Fixed Position.

Generally a user of fixed position and no follow path parenting. As shown in answer here https://blender.stackexchange.com/a/169719/15543 With fixed position can keyframe or drive the offset, such that 0 is start of curve, and 1 is other end.