Object vertices coordinates are returned as an empty list occasionally

Question

I am trying to get the furthest/closest vertices on both the X and Y axis for a mesh object. However, Blender returns empty lists for the coordinates for the same object. I initially thought the mesh has not been loaded into blender but then I realized that although the object has been loaded, I still might get an empty list. I may note that the problem occurs for random meshes and not only for an specific mesh. Below I post the relevant codes:

Here's how I load a mesh:

    obj_file = os.path.join(model_path)
    bpy.ops.import_scene.obj(filepath=obj_file)

###############################################################
## obj file comes as a bunch of different meshes, unify them ##
###############################################################

    obs = []
    for ob in bpy.context.scene.objects:
        # whatever objects you want to join...
        if ob.type == 'MESH':
            obs.append(ob)


    if len(obs) > 1:
        # Join the meshes
        ctx = bpy.context.copy()
        ctx['active_object'] = obs[0]
        ctx['selected_objects'] = obs
        # we need the scene bases as well for joining
        ctx['selected_editable_bases'] = [bpy.context.scene.object_bases[ob.name] for ob in obs]
        bpy.ops.object.join(ctx)


    for ob in bpy.context.selectable_objects:
        #if ob.name.startswith('simplified_model'):
        if ob.type == 'MESH':
            obj = ob            # this is for scoping reasons
            obj.select = True
            bpy.context.scene.objects.active = obj

    if dissolve != None:
        if dissolve:
            # This is to be used for simplifying mesh models
            bpy.ops.object.mode_set(mode='EDIT')
            bpy.ops.mesh.dissolve_limited()
            bpy.ops.object.mode_set(mode='OBJECT')

            obj.collision.use = True

And then setting up the scene:

        bpy.context.scene.render.resolution_x = 448
        bpy.context.scene.render.resolution_y = 448
        bpy.context.scene.render.resolution_percentage = 100

        s = 1.25
        bpy.context.scene.camera.location.x = s
        bpy.context.scene.camera.location.y = s
        bpy.context.scene.camera.location.z = s

        empty = bpy.data.objects.new('empty', None)
        bpy.context.scene.objects.link(empty)
        bpy.context.scene.update()



        camera_follow_constraint = bpy.context.scene.camera.constraints.new(type='TRACK_TO')
        camera_follow_constraint.target = obj #empty
        camera_follow_constraint.track_axis = 'TRACK_NEGATIVE_Z'
        camera_follow_constraint.up_axis = 'UP_Y'

And finally here's how I get the coordinates. Sometimes, the xs or ys lists are returned empty and I haven't been able to find out why:

mat = obj.matrix_world
coords = [mat * vert.co for vert in obj.data.vertices]


xs = [co.x for co in coords]
ys = [co.y for co in coords]

I am using Python 3. I would appreciate if someone can give me some help on this.

Here are two links for two meshes for which I experienced the problem. I may note again that the problem does not only occur for these two models. I have thousands of meshes and each time it occurs for a bunch of them:

Model1 Model2

Thanks

Answer 1

Here is a take on this. Removed the context override on the join op, the import wavefront obj operator returns all imported objects as selected. This is the list context.selected_objects whereas scene.objects is all the objects in the scene. Not sure why you would want to use context.selectable_objects for this case.

Simply deselect if not a mesh, assign first mesh obj as active (if there are mesh objs) , and then call bpy.ops.object.join().

Used bmesh for limited dissolve, takes away the need to pop modes.

Tested fine on object1.obj

import bpy
from bpy import context
scene = context.scene
import bmesh

# make a bmesh
bm = bmesh.new()
dissolve = True
filepath = "/home/batfinger/Downloads/model1.obj"

bpy.ops.import_scene.obj(filepath=filepath)

mesh_objs = []
for o in context.selected_objects:
    if not o.type == 'MESH':
        o.select = False
        print(o.name, "not a mesh")
        continue
    if dissolve:
        # use bmesh to dissolve
        bm.from_mesh(o.data)
        print("Pre dissolve", len(bm.verts))
        geom = bmesh.ops.dissolve_limit(bm, angle_limit=0.082665,
                                        verts=bm.verts,
                                        edges=bm.edges,
                                        delimit=0)
        bm.to_mesh(o.data)
        print("Post dissolve", len(o.data.vertices))
        bm.clear()
    # append the mesh object
    mesh_objs.append(o)
bm.free()
# if no mesh objs do nothing
if mesh_objs:
    scene.objects.active = mesh_objs[0]

    bpy.ops.object.join()
    # newly joined obj
    obj = scene.objects.active
    # look at verts
    verts = obj.data.vertices
    vertsx = [v.co.x for v in verts]
    vertsy = [v.co.y for v in verts]
    print(len(vertsx), len(vertsy))