[Bf-python] Add-on import and enable process

[James Crowther]

Hi there,
	I’m trying to make our add-on work when its enabled from blender starting up (safe as enabled in user prefs). But for some reason this doesn’t work. It works fine when enabled after blender has started. 
The add-on is comprised of a package with sub-packages. The parent package at the upper most level has its __init__ file simply import and call register on the sub packages as required by the environment. We have binaries in our package and so the sub-packages contain different builds for different operating systems. 

The issue is that the top level __init__ file imports the sub package it needs when it is registered (not when its imported), it then calls the imported packages register method (see package structure and code below).
The problem comes when the package is being loaded at run time, its seems that the package is first imported and then register is run, then unregister is run. This causes an issue since the cr_platform object doesn’t seem to exist when the package is unregistered during the enabling of the add-on at load time of blender. 

I wasn’t really expecting the enable process for an add-on to first load then unload and then load the add-on again. I really need to understand this whole process better to be able to either work around the issue or maybe redesign the package if its not compatible? I thought that what I had built didn’t violate anything in the python blender api as far as I can tell. 

Help would be most appreciated!!

James


Package structure 

top_level of package

__init__.py
Darwin
	__init__.py
	bl_2_78
		lib
	bl_2_79
		lib
Linux
	__init__.py
	bl_2_78
		lib
	bl_2_79
		lib
Wind64
	__init__.py
	bl_2_78
		lib
	bl_2_79
		lib
	


### contents of __init__.py at the top level

import bpy, imp, subprocess, sys, os

def select_platform():
    """ checks python/blender versions and sets import paths accordingly
    """
    
                    
    global cr_platform
    
    if sys.platform.startswith('darwin'):
        from . import Darwin as cr_platform
    elif sys.platform.startswith('linux'):
        from . import Linux as cr_platform
    elif sys.platform.startswith('win'):
        from . import Win64 as cr_platform
    else:
        raise RuntimeError(" unsupported version of python, you have :" +\
                python_version +" supported versions are 3.5.2 and 3.5.3") 
        
    

def register():
    
    select_platform()
    
    cr_platform.register()
    
    
def unregister():
    
    if 'cr_platform' in locals():
    
        cr_platform.unregister()
        
    else:
        raise RuntimeError("could not find the cr_platform while unregistering!")

 


if __name__ == '__main__':
    register()