__init__.py

import bpy

"""
###############################################################################
PROPERTY GROUPS: START-UP CONFIGURATION OF DATA IN PANELS UI.
###############################################################################
"""
GroupObjectsData = None


class GroupObjects:
    def __init__(self, blender_objects: bpy.types.bpy_prop_collection = None):
        self.blender_objs = []

        self.data = {}
        if len(blender_objects) > 0:
            for obj in blender_objects:
                if "Group_obj" in obj.name:
                    self.blender_objs.append(obj)

    def add_keypose(self, frame: int):
        bpy.context.scene.frame_current = frame
        frame_name = "frame_" + str(frame)
        self.data[frame_name] = {}

        for obj in self.blender_objs:
            x, y, z = obj.location
            self.data[frame_name][obj.name] = (x, y, z)
            obj.keyframe_insert(data_path="location", frame=frame)


class GroupPosesPropertyGroup_PGT(bpy.types.PropertyGroup):
    frame = bpy.props.IntProperty(name="hui")


class GroupKeyposes_UL(bpy.types.UIList):

    def draw_item(self, context, layout, data, item, icon, active_data, active_propname):
        if self.layout_type in {'DEFAULT', 'COMPACT'}:
            if item:
                row = layout.row()
                row.prop(item, "frame", text="frame_" + str(item.frame))
                row.enabled = False
            else:
                layout.label(text="", translate=False, icon_value=icon)
        elif self.layout_type in {'GRID'}:
            layout.alignment = 'CENTER'
            layout.label(text="", icon_value=icon)


"""
###############################################################################
UI AND PANELS FRONTEND.
###############################################################################
"""


class PanelExmpl_PT(bpy.types.Panel):
    bl_idname = "GroupPosesPanel"
    bl_label = "Group poses"
    bl_space_type = 'VIEW_3D'
    bl_region_type = 'UI'
    bl_category = 'View'
    bl_options = {'DEFAULT_CLOSED'}

    def draw(self, context):
        layout = self.layout
        scene = context.scene

        layout.label(text="Group frames")
        layout.operator('group.add_keypose', text='Add Keypose')
        row1 = layout.row()
        row1.prop(scene, 'current_group_frame')

        row2 = layout.row()
        row2.template_list("GroupKeyposes_UL", "myul_id", scene, "group_created_poses", scene,
                             "current_group_frame")


"""
###############################################################################
BACKEND OF BLENDER PANELS UI.
###############################################################################
"""


class AddKeypose_OT(bpy.types.Operator):
    bl_idname = "group.add_keypose"
    bl_label = "Add Keypose Operator"
    bl_options = {"INTERNAL"}

    def execute(self, context):
        global GroupObjectsData
        if GroupObjectsData is None:
            GroupObjectsData = GroupObjects(bpy.data.objects)
        scene = context.scene
        current_frame = scene.frame_current
        GroupObjectsData.add_keypose(current_frame)
        scene.current_group_frame = current_frame
        keypose = scene.group_created_poses.add()
        keypose.frame = current_frame

        print("INFO: frame {}; \n{}".format(current_frame, GroupObjectsData.data))

        return {"FINISHED"}


"""
###############################################################################
ADDON INFO. REGISTER/UNREGISTER FUNCTIONS.
###############################################################################
"""

bl_info = {
    "name": "EXMPL ADDON",
    "version": (0, 1, 0),
    "blender": (2, 80, 0),
    "location": "View3D > Sidebar > View Tab > Group Poses",
    "warning": "",
    "wiki_url": "",
    "support": "TESTING"
}


def register():
    bpy.types.Scene.current_group_frame = bpy.props.IntProperty(name="current_group_frame")
    bpy.utils.register_class(GroupPosesPropertyGroup_PGT)
    bpy.types.Scene.group_created_poses = bpy.props.CollectionProperty(type=GroupPosesPropertyGroup_PGT)
    bpy.utils.register_class(GroupKeyposes_UL)
    bpy.utils.register_class(AddKeypose_OT)
    bpy.utils.register_class(PanelExmpl_PT)


def unregister():
    del bpy.types.Scene.group_created_poses
    bpy.utils.unregister_class(GroupPosesPropertyGroup_PGT)
    bpy.utils.unregister_class(PanelExmpl_PT)
    bpy.utils.unregister_class(AddKeypose_OT)
    bpy.utils.unregister_class(GroupKeyposes_UL)


if __name__ == '__main__':
    register()