I have a Python code for a GUI app that I need to migrate. Here’s the global structure (it’s a flat-layout):

Project/
|-- format_controllers/
|   |-- __init__.py
|   |-- controller1/
|   |-- controller2/
|-- core/
|   |-- vars.py
|   |-- __init__.py (empty)
|-- Ctrl_App

The module vars.py define global variables, including this one:

global appCache
appCache = None

Then in my __init__.py file, there are many functions made to handle metadata about the main controllers, and the appCache var is finally initialized :

from core import vars
class AppCache():

    # Initialisation
    def __init__(self):
        self.__dataTypeMetaDict = {}
...

# End of AppCache ========================================================

basevars.CtrlCache = ControllerCache()

Finally, in my Ctrl_App (where there is import format_controllers, I have lines like this:

metaInfo = vars.appCache.metaInfoForType(self.config.dataType)

To sum it up, in Ctrl_App, functions from the __init__.py file of the package format_controllers are used on a global variable defined in a module from the core package, initialized to None, and reinitialized to something not null in the same __init__.py.

My problem is that I get errors. Because appCache is initialized to None in the init from the controllers package, in my Ctrl_App I get errors like this:

AttributeError: 'NoneType' object has no attribute 'metaInfoForType'

I’ve tried to redefine the variable in the beginning but at the end it’s the same. I don’t know why the __init__.py file, where the variable is initialized, is not taken into account when I import the package.

Is there an easier, and cleaner way to do that to finally fix this error? I can patch it but just writing global appCache and appCache = ControllerCache() in all the modules that use this variable but

1. I think it’s not clean at all
2. I’m afraid it’s a very unstable solution

Plus there must have been a good reason for the developer to do that this way, unfortunately I can’t get in touch with them or with anybody that could know.

Important to note : The code was written in Python 2.7 and used a lot of deprecated librairies and functions.