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lets say i have a panel and i want to collapse a part if a bool is False

import bpy





class HelloWorldPanel(bpy.types.Panel):

    """Creates a Panel in the Object properties window"""

    bl_label = "Hello World Panel"

    bl_idname = "OBJECT_PT_hello"

    bl_space_type = 'PROPERTIES'

    bl_region_type = 'WINDOW'

    bl_context = "object"



    def draw(self, context):

        layout = self.layout

        # where should i define this bool ? 

        layout.prop(place, "bool")

        if bool is True:

            obj = context.object



            row = layout.row()

            row.label(text="Hello world!", icon='WORLD_DATA')



        row = layout.row()

        row.label(text="Active object is: " + obj.name)







def register():

    bpy.utils.register_class(HelloWorldPanel)





def unregister():

    bpy.utils.unregister_class(HelloWorldPanel)





if __name__ == "__main__":

    register()

Blender 2.8 has sub panels.

As of blender 2.8 can if bl_parent_id is set in a panel it will be appended to the parent panel. Use the usual 'DEFAULT_CLOSED' in the bl_options set to start with panel closed.

This avoids needing to set up some boolean property to open close UI altogether.

Here is a sample file I've been testing for ordering panels. First panel is defined as a child of the object transform panel. Second panel is a child of first. Can unregister and re-register with different parent ids to sort sub-panels, which is what I was testing

The two demo sub panels appended to object transform

import bpy

from bl_ui.properties_object import ObjectButtonsPanel, OBJECT_PT_transform



class LayoutDemoPanel(bpy.types.Panel, ObjectButtonsPanel):

    bl_label = "Layout Demo"

    bl_idname = "SCENE_PT_layout"

    bl_parent_id = 'OBJECT_PT_transform'

    bl_space_type = 'PROPERTIES'

    bl_region_type = 'WINDOW'



    def draw(self, context):

        layout = self.layout



        scene = context.scene



        # Create a simple row.

        layout.label(text=" Simple Row:")



        row = layout.row()

        row.prop(scene, "frame_start")



class LayoutDemoPanel2(bpy.types.Panel, ObjectButtonsPanel):

    bl_label = "Layout Demo 2"

    bl_idname = "SCENE_PT_layout2"

    bl_parent_id = 'SCENE_PT_layout'

    bl_space_type = 'PROPERTIES'

    bl_region_type = 'WINDOW'



    def draw(self, context):

        layout = self.layout



        scene = context.scene



        # Create a simple row.

        layout.label(text=" Simple Row:")



        row = layout.row()

        row.prop(scene, "frame_start")





def register():

    bpy.utils.register_class(LayoutDemoPanel)

    bpy.utils.register_class(LayoutDemoPanel2)



def unregister():

    bpy.utils.unregister_class(LayoutDemoPanel2)

    bpy.utils.unregister_class(LayoutDemoPanel1)





if __name__ == "__main__":

    register()

If you have some logical setting that when set needs more UI How to dynamically show/hide panel elements using python?