Using pluggy without importing anything from host application (the one I'm extending)

app.py

#!/usr/bin/env python
# -*- coding: UTF-8 -*-

'''
My application uses authentication from my framework
My application also extends framework using a plugin defined in plug.py

Everything works fine. But the plugin needs to import the host app (framework)
or maybe I'm missing something.
'''

import framework
import plug


if __name__ == '__main__':
    plug.setup_plugin()
    auth = framework.Authenticate()
    auth.authenticate()

framework.py

# -*- coding: UTF-8 -*-

'''
Framework provides simple functionality - authentication
which has one hook point - before_authenticate()
'''

import pluggy


plug_name = 'myapp'
hookspec = pluggy.HookspecMarker(plug_name)
hookimpl = pluggy.HookimplMarker(plug_name)
plug_mgr = pluggy.PluginManager(plug_name)


class PluginSpec(object):
    @hookspec
    def before_authenticate(self, param1):
        '''Hook that can be customized.'''


plug_mgr.add_hookspecs(PluginSpec())


class Authenticate(object):
    def authenticate(self):
        print('APP: calling plugins before_authenticate()')
        results = plug_mgr.hook.before_authenticate(param1='value1')
        print('APP: results from plugins:', results)

plug.py

# -*- coding: UTF-8 -*-

import framework


class AuthPlugin1(object):
    @framework.hookimpl
    def before_authenticate(self, param1):
        print('PLUGIN 1: before_authenticate(), param: {}'.format(param1))
        return 'before_1'


def setup_plugin():
    # To register a plugin, I need a direct access to PluginManager instance.
    # Therefore I need to import it from framework:
    pm = framework.plug_mgr

    # However, if there was a way to get PluginManager instance for example
    # like python logging returns loggers: mylog = logging.getLogger('mylog')
    # then I could do something like:
    # import pluggy
    # pm = pluggy.get_pluggin_manager('myapp')
    # without importing framework I'm extending
    # and then:
    pm.register(AuthPlugin1())


'''
This also leads me to thoughts - if I want to write a plugin without importing
the host application (the framework in my case), I need a PluginManager
instance and hookimpl decorator as well.

To define a plugin something like these functions would be needed:

plug_mgr = pluggy.get_pluggin_manager('myapp')
and
hookimpl = pluggy.get_hookimpl_marker('myapp')
'''

@dwich see my gitter explanation.

if I want to write a plugin without importing
the host application (the framework in my case), I need a PluginManager
instance and hookimpl decorator as well.

Or, you can use the setuptools entry points system natively supported in pluggy.

Hope that helps 👍