unclear error message

[Peter230655]

To visualise the results of an animation (written using sympy.physics.mechanics) I have this cell in the Jupyter notebook:

start6 = time.time()

times1 = []
resultat1 = []

#=======================
zeitpunkte = 500
#=======================

reduction = max(1, int(len(times)/zeitpunkte))

for i in range(len(times)):
    if i % reduction == 0:
        times1.append(times[i])
        resultat1.append(resultat[i])

schritte1 = len(times1)
resultat1 = np.array(resultat1)
times1 = np.array(times1)
print('number of points considered:',len(times1))

Dmc_loc = [[me.dot(punkt.pos_from(P[0]), uv) for uv in N] for punkt in Dmc]
punkt_loc = [[me.dot(punkt.pos_from(P[0]), uv) for uv in N] for punkt in Po]
Dmc_loc_lam = sm.lambdify(qL + pL, Dmc_loc, cse=True)
punkt_loc_lam = sm.lambdify(qL + pL, punkt_loc, cse=True)


winkel = sm.symbols('winkel')
Rotation1 = sm.Matrix([[sm.cos(winkel), -sm.sin(winkel), 0], [sm.sin(winkel), sm.cos(winkel), 0], [0., 0., 1]])
Rot_lam = sm.lambdify(winkel, Rotation1.T)
Rotation = Rot_lam(np.pi/2.)

TC_store = []
TR_store = []
TP_store = []
body_mesh_store = []
track_store = []
farben = ['orange', 'blue', 'green', 'yellow', 'red']

laengen = l1

# the list of frames A contains the inertial frame A[0] = N. This must not be here
AB = copy(A) # for whatever reason, deepcopy does not work here
AB.pop(0)

for i in range(n):
#for its mass center
    TC = sm.eye(4)
    TC[:3, :3] = (AB[i].dcm(N)) * Rotation
    TC = TC.reshape(16, 1)
    TC_lam = sm.lambdify(qL + pL, TC)   

    TR = sm.eye(4)
    TR[:3, :3] = (AB[i].dcm(N)) * Rotation
    TR = TR.reshape(16, 1)
    TR_lam = sm.lambdify(qL + pL, TR) 
    
    TP = sm.eye(4)
    TP[:3, :3] = (AB[i].dcm(N)) * Rotation
    TP = TP.reshape(16, 1)
    TP_lam = sm.lambdify(qL + pL, TP) 


# store the information about the body, expressed in TAc for every time step.
    TCs = []   # for the ball
    TRs = []   # for the rod
    TPs = []   # for the red dot
    
# Create the TAs, containing 'one TA' for each time step
# resultat contains the results of the numeric integration. 
# where the numeric integration was evaluated
    for k_1 in range(resultat1.shape[0]):
        zeit = times[i]
        TCi = TC_lam(*[resultat1[k_1, l] for l in range(resultat1.shape[1])], *pL_vals)  # the balls
        TRi = TR_lam(*[resultat1[k_1, l] for l in range(resultat1.shape[1])], *pL_vals)  # the rod
        TPi = TP_lam(*[resultat1[k_1, l] for l in range(resultat1.shape[1])], *pL_vals)  # the dot

# TAi[12], TAi[13], TAi[14] hold the location of A[i] w.r.t. N.
# As the axis chosen for solving the equations of motion, and the axis given by pythreejs do not 
# coincide, the values for TAi[..] must be permutated accordingly.
# of course here different locations for center of ball and center of mass.
        TRi[12] = -Dmc_loc_lam(*[resultat1[k_1, l] for l in range(resultat1.shape[1])], *pL_vals)[i][1]
        TRi[13] =  Dmc_loc_lam(*[resultat1[k_1, l] for l in range(resultat1.shape[1])], *pL_vals)[i][0]
        TRi[14] =  Dmc_loc_lam(*[resultat1[k_1, l] for l in range(resultat1.shape[1])], *pL_vals)[i][2]
    
        TCi[12] = -Dmc_loc_lam(*[resultat1[k_1, l] for l in range(resultat1.shape[1])], *pL_vals)[i][1]
        TCi[13] =  Dmc_loc_lam(*[resultat1[k_1, l] for l in range(resultat1.shape[1])], *pL_vals)[i][0]
        TCi[14] =  Dmc_loc_lam(*[resultat1[k_1, l] for l in range(resultat1.shape[1])], *pL_vals)[i][2] 

        TPi[12] = -punkt_loc_lam(*[resultat1[k_1, l] for l in range(resultat1.shape[1])], *pL_vals)[i][1]
        TPi[13] =  punkt_loc_lam(*[resultat1[k_1, l] for l in range(resultat1.shape[1])], *pL_vals)[i][0]
        TPi[14] =  punkt_loc_lam(*[resultat1[k_1, l] for l in range(resultat1.shape[1])], *pL_vals)[i][2]

        TRs.append(TRi.squeeze().tolist())
        TCs.append(TCi.squeeze().tolist())
        TPs.append(TPi.squeeze().tolist())
       
    TC_store.append(TCs)
    TR_store.append(TRs)
    TP_store.append(TPs)
    
# Create the objects, which will move
# 1. The ball
    body_geom_C = p3js.SphereGeometry(r1, 12, 12)
    body_material_C = p3js.MeshStandardMaterial(color=farben[i], wireframe=False)
    body_mesh_C = p3js.Mesh(geometry=body_geom_C, material=body_material_C, name='ball_' + str(i))

# 2. Rod
    body_geom_R = p3js.CylinderGeometry(radiusTop=0.05, radiusBottom=0.05, height=laengen[i], 
                    radialSegments=6, heightSegments=10, openEnded=False)
    body_material_R = p3js.MeshStandardMaterial(color='black', wireframe=False)
    body_mesh_R = p3js.Mesh(geometry=body_geom_R, material=body_material_R, name='rod_' + str(i))
    
# 3. the dot    
    body_geom_P = p3js.SphereGeometry(0.25, 12, 12)
    body_material_P = p3js.MeshStandardMaterial(color='red', wireframe=False)
    body_mesh_P = p3js.Mesh(geometry=body_geom_P, material=body_material_P, name='punkt_' + str(i))

# locate the body in 3D space and add the coordinate system of the body
    body_mesh_R.matrixAutoUpdate = False
    body_mesh_R.add(p3js.AxesHelper(0.1))  # length of the axis of the ball system A2
    body_mesh_R.matrix = TR_store[i][0]             # starting point of the animation

    body_mesh_C.matrixAutoUpdate = False
    body_mesh_C.add(p3js.AxesHelper(0.01))    # length of the axis of the center of mass system A2
    body_mesh_C.matrix = TC_store[i][0]          # starting point of the animation
    
    body_mesh_P.matrixAutoUpdate = False
    body_mesh_P.add(p3js.AxesHelper(0.01))    # length of the axis of the center of mass system A2
    body_mesh_P.matrix = TP_store[i][0]          # starting point of the animation
    
    
    body_mesh_store.append(body_mesh_C)
    body_mesh_store.append(body_mesh_R)
    body_mesh_store.append(body_mesh_P)
    

# Create the 'picture'.
# all the 'paramters' are taken by trial and error.
view_width = 1200
view_height = 400

# Values just found by trial an error.
p1, p2 = 5, 5
if n == 2:
    p3 = 18
elif n == 3:
    p3 = 22
else:
    p3 = 30

camera = p3js.PerspectiveCamera(position=[p1, p2, p3],
                                up=[-1.0, 0.0, 0.0],
                                aspect=view_width/view_height)

key_light = p3js.DirectionalLight(position=[0, 0, 10])
ambient_light = p3js.AmbientLight()

axes = p3js.AxesHelper(20)

children = []
for i in range(3*n):
    children = children + [body_mesh_store[i], axes, camera, key_light, ambient_light]

scene = p3js.Scene(children=children)
controller = p3js.OrbitControls(controlling=camera)
renderer = p3js.Renderer(camera=camera, scene=scene, controls=[controller],
                         width=view_width, height=view_height)

# Create the action, simply copied from JM's lecture.

for i in range(n):
    eigenname = 'ball_'+str(i)
    track_C = p3js.VectorKeyframeTrack(
        name="scene/" + eigenname + ".matrix",
        times=times1,
        values=TC_store[i])
    
    eigenname = 'rod_' + str(i)
    track_R = p3js.VectorKeyframeTrack(
        name="scene/" + eigenname + ".matrix",
        times=times1,
        values=TR_store[i])
    
    eigenname = 'punkt_' + str(i)
    track_P = p3js.VectorKeyframeTrack(
        name="scene/" + eigenname + ".matrix",
        times=times1,
        values=TP_store[i])
    
    track_store += [track_C] + [track_R] + [track_P]

duration = times1[-1] - times1[0]
clip = p3js.AnimationClip(tracks=track_store, duration=duration)
action = p3js.AnimationAction(p3js.AnimationMixer(scene), clip, scene)

# avoid error if the animation has not run before this runs.
if start5 != None:
    print(' it tooks {:.3f} sec to run the complete program'.format(time.time() - start6 + start5 - start ))

renderer

I get this error message:

---

TraitError Traceback (most recent call last)
File c:\Users\Peter\anaconda3\envs\math\Lib\site-packages\ipywidgets\widgets\widget.py:766, in Widget._handle_msg(self, msg)
764 if 'buffer_paths' in data:
765 _put_buffers(state, data['buffer_paths'], msg['buffers'])
--> 766 self.set_state(state)
768 # Handle a state request.
769 elif method == 'request_state':

File c:\Users\Peter\anaconda3\envs\math\Lib\site-packages\ipywidgets\widgets\widget.py:648, in Widget.set_state(self, sync_data)
645 if name in self.keys:
646 from_json = self.trait_metadata(name, 'from_json',
647 self._trait_from_json)
--> 648 self.set_trait(name, from_json(sync_data[name], self))

File c:\Users\Peter\anaconda3\envs\math\Lib\site-packages\traitlets\traitlets.py:1738, in HasTraits.set_trait(self, name, value)
1736 raise TraitError(f"Class {cls.name} does not have a trait named {name}")
1737 else:
-> 1738 getattr(cls, name).set(self, value)

File c:\Users\Peter\anaconda3\envs\math\Lib\site-packages\traitlets\traitlets.py:703, in TraitType.set(self, obj, value)
702 def set(self, obj, value):
--> 703 new_value = self._validate(obj, value)
704 try:
705 old_value = obj._trait_values[self.name]

File c:\Users\Peter\anaconda3\envs\math\Lib\site-packages\traitlets\traitlets.py:735, in TraitType._validate(self, obj, value)
733 return value
734 if hasattr(self, "validate"):
--> 735 value = self.validate(obj, value)
736 if obj._cross_validation_lock is False:
737 value = self._cross_validate(obj, value)

File c:\Users\Peter\anaconda3\envs\math\Lib\site-packages\traitlets\traitlets.py:2302, in Union.validate(self, obj, value)
2300 except TraitError:
2301 continue
-> 2302 self.error(obj, value)

File c:\Users\Peter\anaconda3\envs\math\Lib\site-packages\traitlets\traitlets.py:841, in TraitType.error(self, obj, value, error, info)
835 else:
836 e = "The '{}' trait expected {}, not {}.".format(
837 self.name,
838 self.info(),
839 describe("the", value),
840 )
--> 841 raise TraitError(e)

TraitError: The 'target' trait of a DirectionalLight instance expected an Uninitialized or an Object3D, not the str 'IPY_MODEL_3f5c3aea-5803-4ed3-9aa5-c7d9447925e9'.

The animation still works as expected, so my question is really more curiosity.
Thanks a lot for any help!!