Issues with module imports going from python 2 to python 3

Question

I am trying to upgrade a 10 year old event listener that I didn't write from Python 2.7 to python 3.7. The basic issue I'm running into is the way the original script was importing its plugins. The idea behind the original script was that any python file put into a "plugins" folder, with a "registerCallbacks" function inside it would auto-load itself into the event listener and run. It's been working great for lots of studios for years, but Python 3.7 is not liking it at all.
The folder structure for the original code is as follows:

EventListenerPackage
    src
        event_listener.py
    plugins
        plugin_1.py
        plugin_2.py

From this, you can see that both the event listener and the plugins are held in folders that are parallel to each other, not nested.
The original code read like this:

# Python 2.7 implementation

import imp

class Plugin(object):
    def __init__(self, path):
        self._path = 'c:/full/path/to/EventListenerPackage/plugins/plugin_1.py'
        self._pluginName = 'plugin_1'

    def load(self):
        try:
            plugin = imp.load_source(self._pluginName, self._path)
        except:
            self._active = False
            self.logger.error('Could not load the plugin at %s.\n\n%s', self._path, traceback.format_exc())
            return

        regFunc = getattr(plugin, 'registerCallbacks', None)

Due to the nature of the changes (as I understand them) in the way that Python 3 imports modules, none of the other message boards seem to be getting me to the answer.
I have tried several different approaches, the best so far being:
How to import a module given the full path?
I've tried several different methods, including adding the full path to the sys.path, but I always get "ModuleNotFoundError".
Here is roughly where I'm at now.

import importlib.util
import importlib.abc
import importlib

class Plugin(object):
    def __init__(self, path):
        self._path = 'c:/full/path/to/EventListenerPackage/plugins/plugin_1.py'
        self._pluginName = 'plugin_1'

    def load(self):
        try:
            spec = importlib.util.spec_from_file_location('plugins.%s' % self._pluginName, self._path)
            plugin = importlib.util.module_from_spec(spec)
            # OR I HAVE ALSO TRIED
            plugin = importlib.import_module(self._path)
        except:
            self._active = False
            self.logger.error('Could not load the plugin at %s.\n\n%s', self._path, traceback.format_exc())
            return

        regFunc = getattr(plugin, 'registerCallbacks', None)

Does anyone have any insights into how I can actually import these modules with the given folder structure? Thanks in advance.

Answer 1

You're treating plugins like it's a package. It's not. It's just a folder you happen to have your plugin source code in.

You need to stop putting plugins. in front of the module name argument in spec_from_file_location:

spec = importlib.util.spec_from_file_location(self._pluginName, self._path)

Aside from that, you're also missing the part that actually executes the module's code:

spec.loader.exec_module(plugin)

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Depending on how you want your plugin system to interact with regular modules, you could alternatively just stick the plugin directory onto the import path:

sys.path.append(plugin_directory)

and then import your plugins with import or importlib.import_module. Probably importlib.import_module, since it sounds like the plugin loader won't know plugin names in advance:

plugin = importlib.import_module(plugin_name)

If you do this, plugins will be treated as ordinary modules, with consequences like not being able to safely pick a plugin name that collides with an installed module.

---

As an entirely separate issue, it's pretty weird that your Plugin class completely ignores its path argument.